JP4110482B2 - Laminated polyester film and specular reflection film - Google Patents

Description

  The present invention relates to a laminated polyester film and a specular reflection film using the same. More specifically, a laminated polyester that can be suitably used as a substrate of a specular reflection film formed with a light reflection layer composed of a metal thin film layer, particularly as a surface light source reflector of a liquid crystal display (hereinafter abbreviated as LCD). The present invention relates to a film and a specular reflection film using the film.

  In recent years, the use of liquid crystal screens has been remarkably expanded, and in addition to conventional notebook personal computers, they have been widely used in stationary personal computers, liquid crystal televisions, mobile phone displays, and various game machines. In response to such expanded applications, higher brightness and higher definition of the screen are desired, and improvements such as higher output and increased number of light source lamps have been made even for illumination light sources. In addition, with respect to the reflector used in the light source, the demand for its reflection characteristics has been advanced. In particular, there is an increasing demand for higher brightness in the market.

  In order to satisfy the demand for higher brightness, it is preferable to use a reflector that uses mirror reflection of a metal thin film layer such as silver or aluminum. However, this method is strong in specular reflection light and can increase the brightness, but hardly reflects light at other angles with respect to the incident angle of light. Therefore, when it is used as a reflector for LCD, a phenomenon occurs that it is bright only when viewed from a certain direction and is dark and difficult to see when viewed from another angle. This phenomenon is generally called high directivity or narrow viewing angle. For this reason, conventionally, a method has been used in which specular reflection light with high directivity is reduced and diffuse reflection light with low directivity is increased.

For example, the following method is disclosed.
(1) A light reflecting layer made of a metal thin film is laminated on the opposite side of the reflective surface of a resin film substrate containing white inorganic particles such as titanium dioxide, and diffuse reflected light is increased by the light scattering effect of the inorganic particles. (For example, refer to Patent Documents 1 to 7)
(2) On the surface of the light reflection layer made of a silver-based metal thin film, a film containing a white pigment or a film in which a resin layer containing a white pigment is laminated is superimposed, and diffuse reflected light is emitted by the light scattering effect of the white pigment. Method of increasing (for example, see Patent Documents 8 to 9)
(3) A method in which a light reflecting layer made of a silver thin film layer is formed on a flat surface opposite to a matted surface of a transparent film having a matted surface, and diffuse reflected light is increased by a light scattering effect on the matted surface. (For example, see Patent Document 10)
(4) An ultraviolet absorber and a white pigment as required are used to form a light reflecting layer composed of a silver thin film layer on a matte film having a specific haze, and the ultraviolet absorber or white pigment in the film Method for increasing diffuse reflected light by scattering action of light beam (for example, see Patent Document 11)

(5) A resin layer containing particles is laminated on the surface of the base film, an uneven layer is formed on the surface of the base film, and a light reflecting layer made of silver or an aluminum-based metal thin film is provided on the surface of the uneven film. Method of increasing diffuse reflection light by unevenness of reflection layer (for example, see Patent Documents 12 to 14)
(6) A method of increasing the diffuse reflected light by laminating an anchor layer on the surface of the substrate film, forming a light reflecting layer made of a metal vapor deposition layer thereon, and heat-treating under specific conditions (for example, Patent Document 15) reference)
(7) By laminating a metal film on a transmitted light scattering control film composed of a thermoplastic polymer resin oriented film containing a large number of fine pores inside, and by entering light from the film side, depending on the incident direction Method for controlling scattering properties (see, for example, claims of Patent Document 16, paragraphs 0005 and 0060)

JP-A-5-301319 JP-A-10-730 Japanese Patent Laid-Open No. 10-731 Japanese Patent Laid-Open No. 10-732 JP-A-10-67067 JP-A-5-301318 JP-A-10-193494 JP-A-6-15775 JP-A-6-47870 JP-A-8-76112 Japanese Patent Laid-Open No. 7-108643 JP 2001-296410 A JP 2001-350004 A JP 2002-79605 A JP 2000-187207 A Japanese Patent Laid-Open No. 10-332911

  The above method is an effective method for solving the problem that directivity is strong, but the regular reflectance, which is specular reflection light, is reduced, so that the luminance is lowered. For this reason, there is a problem that the demand for high brightness cannot be sufficiently satisfied.

  In recent years, the performance of lens films and light diffusing films incorporated in light sources for LCDs has been improved, and the problem that the viewing angle is narrowed even when a reflector with strong specular reflection is used has been improved. In conjunction with this, there has been an increasing demand for reflectors for high brightness using light reflection made of a metal thin film having strong specular reflection light, that is, regular reflection light. However, when the metal thin film layer is formed on the general-purpose film surface as described above, the required characteristics of the market cannot be sufficiently satisfied in the reflected light intensity and the uniformity thereof, and the required characteristics are improved. There is a strong demand for the development of a base film.

  On the other hand, in general, the metal thin film layer of the specular reflection film is formed by a dry coating method such as vapor deposition or sputtering for metal atoms. However, in the case of industrial production by this method, a pin hole or the like is formed on the metal thin film layer. It becomes difficult to avoid the occurrence of optical defects. In addition, as the thickness of the metal thin film layer varies within the same product, there may be a difference in the light reflectivity depending on the position of the obtained product. In addition, there may be a difference in the light reflectance even within a single reflection film. For this reason, there has been a strong demand for a method for suppressing the fluctuation of the characteristics.

  Further, in recent years, there has been a demand for further improvement in light reflectivity, and a method of increasing the thickness of the metal thin film layer or the like is used in order to satisfy the demand and improve the above-mentioned problems. However, increasing the thickness of the metal thin film layer increases the manufacturing cost. On the other hand, as another method for increasing the light reflectivity, there is a method using a silver-based metal thin film layer having a high light reflectivity, but the silver-based metal thin film layer is expensive.

  Therefore, establishment of a technique capable of maintaining high light reflectance even when the thickness of the metal thin film layer is reduced is strongly demanded in the market.

  An object of the present invention is to provide a specular reflection film having a metal thin film layer as a reflection surface, which can provide a high degree of uniform light reflectivity, in particular, a laminated polyester film suitable as a substrate for a surface light source reflection film for LCD, and The object is to provide a specular reflection film used.

The laminated polyester film of the present invention and the specular reflection film using the same, which can solve the above problems, have the following configuration.
That is, the first invention of the present invention is a laminated polyester film having a layer structure of surface layer (A) / white light-shielding layer (B), wherein the white light-shielding layer (B) is hollow or inorganic inside. The surface layer (A) is a smooth layer made of polyester having a three-dimensional ten-point average roughness (SRz) of 0.23 μm or less, including a polyester composition containing at least one of particles. Ri der light transmittance of 20% or less of the polyester film, and the laminated polyester film, at no load condition, the curl value after heat treatment at 110 ° C. 30 minutes and wherein der Rukoto below 1mm It is a laminated polyester film.

The second invention is a laminated polyester film comprising a layer structure of surface layer (A) / white light-shielding layer (B), wherein the white light-shielding layer (B) contains at least cavities or inorganic particles therein. The surface layer (A) is a smooth layer made of a polyester containing no polyester or a particle content of 50 ppm or less, and the light transmittance of the laminated polyester film. der than 20% is, and the laminated polyester film, at no load condition, the curl value after heating for 30 minutes at 110 ° C. is a laminated polyester film characterized in der Rukoto below 1 mm.

  3rd invention contains the cavity made to express by extending | stretching the polyester composition containing polyester and a polyester resin incompatible with this polyester at least to one direction inside the said white light-shielding layer (B) A laminated polyester film according to the first or second invention.

A fourth invention is the laminated polyester film according to the first or second invention, wherein an apparent density of the laminated polyester film is 0.60 to 1.35 g / cm ³ .

  A fifth invention is characterized in that the three-dimensional ten-point average roughness (SRz) of the surface of the white light-shielding layer (B) is more than 0.23 μm and not more than 3.0 μm. It is a laminated polyester film as described in the invention.

  6th invention is 75-300 micrometers in total thickness of the said laminated polyester film, and is 5-30 micrometers in thickness of a surface layer (A), The laminated polyester as described in 1st or 2nd invention characterized by the above-mentioned. It is a film.

  According to a seventh aspect of the present invention, the laminated polyester film has a layer configuration of at least three layers of a surface layer (A) / white light-shielding layer (B) / surface layer (C), and the surface layer (C) is a resin. In the first or second invention, the SRz of the surface layer (C) is larger than the SRz of the surface layer (A) and is 2.0 μm or less. The laminated polyester film described.

  In an eighth aspect of the invention, the laminated polyester film has a layer structure of surface layer (A) / white light-shielding layer (B) / polyester layer (A ′) / surface layer (C), and the surface layer (C ) Is a coating layer (C ′) containing a resin and particles, and the polyester layer (A ′) is made of polyester containing no particles or having a particle content of 100 ppm or less. It is a laminated polyester film as described in the invention.

  According to a ninth aspect, in the eighth aspect, the coating layer (C ′) contains particles a having an average particle size of 20 nm or more and less than 150 nm and particles b having an average particle size of 150 nm or more and 600 nm or less. It is a laminated polyester film.

  In a tenth aspect of the present invention, the total thickness of the laminated polyester film is 100 to 300 μm, the thickness of the surface layer (A) is 5 to 30 μm, the thickness of the surface layer (C), or the polyester layer (A ′) The total thickness of the coating layer (C ′) and the coating layer (C ′) is 5 to 30 μm.

In an eleventh aspect of the invention, when the laminated polyester film is heat-treated at 170 ° C. for 20 minutes, the occupation area ratio of particles deposited on the surface opposite to the surface layer (A) of the laminated polyester film is 0.008 μm ² / μm. The laminated polyester film according to any one of the first, second, seventh, and eighth inventions, wherein the laminated polyester film is ² or less.

In the twelfth invention, the surface layer (A) and the white light-shielding layer (B), the surface layer (A) and the surface layer (C), or the surface layer (A) and the coating layer (C ′) of the laminated polyester film are combined. The laminated polyester film according to any one of the first, second, seventh, and eighth inventions, wherein a static friction coefficient when superposed is 0.60 or less.

A thirteenth invention uses the laminated polyester film according to any one of the first, second, seventh, and eighth inventions as a base material for a specular reflection film in which a metal thin film layer is laminated on a surface layer (A) of the film. A laminated polyester film for a specular reflection film, wherein a metal thin film layer irradiated with light is used as a reflection surface.

A fourteenth invention is a specular reflection film having a metal thin film layer irradiated with light as a reflection surface, the surface layer (A of the laminated polyester film according to any one of the first, second, seventh and eighth inventions). ) And a metal thin film layer.

  Since the laminated polyester film of the present invention can increase the light reflectivity by forming a light reflection layer comprising a metal thin film layer on the surface layer (A) excellent in smoothness, a high-brightness specular reflection film is used. Obtainable.

  In addition, since the laminated polyester film of the present invention can utilize the light reflection function of the white light-shielding layer (B), when the metal thin film layer is provided on the surface layer (A), the thickness of the metal thin film layer varies. Also, the non-uniformity of the specular reflection light can be suppressed. Further, even if the thickness of the metal thin film layer is reduced, high reflected light can be obtained, which is economically advantageous. Furthermore, even if there is a pinhole in the metal thin film layer, since the light transmitted through the pinhole is reflected by the white light-shielding layer (B), it is possible to prevent the reflected light from being lowered at the pinhole portion.

  Moreover, in this invention, by setting it as the structure which contained the cavity inside the said white light-shielding layer (B), a laminated polyester film can also be reduced in weight besides the light-shielding property provision by a cavity.

  Moreover, since the laminated polyester film of this invention makes the average surface roughness of the surface of the white light-shielding layer (B) opposite the smooth surface layer (A) larger than the smooth surface layer (A). It has excellent handling properties (sliding properties, winding properties, scratch resistance) during film production and processing. Therefore, the film handling process is good in the film manufacturing process and the metal thin film layer forming process, and the surface layer (A) has improved scratch resistance and flatness in these processes. Therefore, it is possible to reduce a decrease in light reflectance when a metal thin film layer is formed on the surface layer (A).

  Moreover, in preferable embodiment of the laminated polyester film of this invention, generation | occurrence | production of the curl by heating is suppressed and it is excellent also in handleability.

  Further, in another preferred embodiment of the laminated polyester film of the present invention, the precipitation of low molecular weight substances composed of low-polymerization oligomers and monomers such as cyclic trimers contained in polyester when the laminated polyester film is heat-treated is suppressed. Therefore, the surface of the surface layer (A) at the time of processing for laminating the metal thin film layer on the laminated film and the processing of the undercoat and overcoat performed before and after the processing, and the storage before and after these processing , Because the contamination due to the transfer of deposited particles from the other surface to the surface of the metal thin film layer during film winding is reduced, the occurrence of defects in the metal thin film layer caused by the surface contamination and the decrease in light reflectance are reduced Is done.

(Laminated polyester film)
The laminated polyester film of the present invention is a laminated polyester film including a layer structure of a surface layer (A) / white light shielding layer (B), and the white light shielding layer (B) has at least cavities or inorganic particles therein. The surface layer (A) is a smooth layer made of polyester having a three-dimensional ten-point average roughness (SRz) of 0.23 μm or less, and a laminated polyester film. The light transmittance is 20% or less.

  Moreover, when expressed from the viewpoint of the composition, the surface layer (A) of the laminated polyester film of the present invention is also a smooth layer made of polyester that does not contain particles or has a particle content of 50 ppm or less.

  A typical layer structure of the laminated polyester film of the present invention is shown in FIG. Moreover, as another suitable embodiment, the layer structure of the laminated polyester film which consists of surface layer A (smooth layer) / white light-shielding layer B / surface layer C (slidable layer) is shown in FIG. Further, FIG. 3 shows a layer structure of a laminated polyester film composed of surface layer A (smooth layer) / white light-shielding layer B / polyester layer A ′ / coating layer C ′ (sliding layer).

  When the laminated polyester film of the present invention is composed of two layers of surface layer A (smooth layer) / white light shielding layer B, the thickness of the laminated polyester film is preferably 75 to 300 μm. Also, surface layer A (smooth layer) / white light-shielding layer B / surface layer (B), or surface layer A (smooth layer) / white light-shielding layer B / polyester layer A ′ / coating layer C ′ (sliding layer) Thus, when it consists of a layer structure of at least 3 layers or more, it is preferable that the thickness of a laminated polyester film is 100-300 micrometers.

  The lower limit of the thickness of the laminated polyester film is more preferably 150 μm, and particularly preferably 170 μm. On the other hand, the upper limit of the thickness is more preferably 250 μm. If the thickness of the laminated film is less than 75 μm (two-layer structure) or less than 100 μm (at least three-layer structure), the film becomes weak and, for example, when it is incorporated into a final product such as an LCD as a light reflector, handling properties decrease. It becomes easy to do. On the other hand, when the thickness of the laminated film exceeds 300 μm, it is economically disadvantageous from the viewpoint of productivity. In addition, the thickness of the base material currently used for the reflecting plate generally used for LCD is 188 micrometers now.

  The polyester constituting the surface layer (A) and the white light-shielding layer (B) of the laminated polyester film of the present invention is at least one aromatic dicarboxylic acid or ester thereof selected from terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, etc. And a polyester produced by polycondensation of at least one glycol selected from ethylene glycol, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and the like. In addition to the direct weight method in which an aromatic dicarboxylic acid and a glycol are directly reacted, these polyesters can be transesterified by an alkyl ester of an aromatic dicarboxylic acid and a glycol and then subjected to a polycondensation, or an aromatic method. It can be produced by a method such as polycondensation of diglycol ester of dicarboxylic acid. The same applies to the case where the surface layer (C) contains polyester or the polyester constituting the polyester layer (A ′).

  Typical examples of the polyester include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate. The polyester may be a homopolymer or a copolymer of a third component. Among these polyesters, a polyester having an ethylene terephthalate unit, a trimethylene terephthalate unit, or an ethylene-2,6-naphthalate unit of 70 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more is preferable. The polyester constituting each layer may be the same type or different type, but the same type is preferable from the viewpoint of curling suppression and economy.

  The laminated polyester film of the present invention is preferably a biaxially oriented polyester film from the viewpoint of mechanical strength and thermal dimensional stability.

(White light shielding layer B)
Conventionally, in a specular reflection film composed of a metal thin film layer / base film and having a metal thin film layer irradiated with light as a reflection surface, the light is reflected by the metal thin film layer. Transparent films have been commonly used. However, the present inventors have newly found that due to the variation in the thickness of the metal thin film layer, light is transmitted through the thin portion of the metal thin film layer and the reflectance of the specular reflection film is lowered. This is an important technical background that has led to the completion of the present invention.

  In the present invention, when the white light-shielding layer (B) is provided with the metal thin film layer on the surface layer (A), even if the metal thin film layer has a thickness variation, the reflectance variation is small in any place, And it is provided in order to maintain a high reflectance. In addition, the specular reflection film of the present invention can return light leaked through the metal thin film layer as reflected light even if the thickness of the metal thin film layer is reduced by providing the base film with light shielding properties. . That is, in the specular reflection film of the present invention, the white light-shielding layer (B) suppresses the variation or decrease in reflectance even when the thickness of the metal thin film layer varies or the thickness of the metal thin film layer is small. This is a functional layer.

  The white light-shielding layer (B) is a layer composed of a resin composition containing at least one of voids or inorganic particles in polyester, and is indispensable for making the light transmittance of the laminated polyester film 20% or less. Layer.

  In the laminated polyester film of the present invention, it is important that the light transmittance, which is one of the light-shielding indexes, is 20% or less, preferably 15% or less, particularly preferably 10% or less. On the other hand, the lower limit of the light transmittance of the laminated polyester film is 0.5% because of the balance between the saturation of the effect of suppressing the fluctuation or decrease in reflectance due to the provision of light shielding properties and the point of mechanical properties and economy. Preferably, 3% is sufficient for practical use.

  When the light transmittance of the laminated polyester film exceeds 20%, that is, the light shielding property is inferior, the reflection effect of light transmitted through the metal thin film layer in the white light shielding layer (B) is likely to be reduced, so the thickness of the metal thin film layer When the thickness fluctuates, or when the thickness of the metal thin film layer is reduced, the function of complementing the reflectance by the white light-shielding layer (B) is lowered. In that case, unless the thickness of the metal thin film layer is increased, high reflected light cannot be obtained, which is economically disadvantageous.

  In addition, when the light transmittance exceeds 20%, when used as a light reflecting film in which a metal thin film layer is formed on the laminated polyester film of the present invention, the metal thin film layer is difficult to avoid when forming the metal thin film layer. It is difficult to block the light transmitted from the generated pinhole with the white light shielding layer (B) and return it from the pinhole again.

  In order to make the light transmittance of the laminated polyester film 20% or less, it is preferable that the void content of the white light-shielding layer (B) and the content of inorganic particles are in the ranges described below. Further, the light transmittance is thickness dependent. That is, even if the white light-shielding layer (B) is the same resin composition, when the thickness of the white light-shielding layer (B) is reduced, the light transmittance increases and the light-shielding property decreases. When the thickness of) increases, the light transmittance decreases and the light shielding property is improved.

  The layer thickness of the laminated polyester film is generally in the range of 75 to 300 [mu] m, preferably 100 to 300 [mu] m, and is generally determined by the application and standard when used in the market. On the other hand, the thickness of the surface layer (A) is set to, for example, 5 to 30 μm within a range in which cavities and particles existing in the white light-shielding layer (B) do not adversely affect the smoothness of the surface layer (A). The Moreover, even if the thickness of the surface layer (A) is too thick, the effect of surface smoothness is saturated. If the thickness of the surface layer (A) needs to exceed 30 μm, the white light-shielding layer can maintain the light-shielding property even if the white light-shielding layer (B) is thin. It is important to design (B).

  Specifically, it is preferable to increase the void content of the white light-shielding layer (B) and the content of inorganic particles within the following ranges. If this is insufficient, for example, a method of containing particles in a resin that is incompatible with the polyester that serves as a cavity developing agent, a white light-shielding layer (B) as a laminated structure, and a large amount of inorganic particles are contained. A special method capable of maintaining high concealability even when the thickness is thin, such as a method of laminating a thin layer, a method of using a color pigment other than white, such as carbon black or a blue pigment, may be used.

  Moreover, since white does not absorb visible light, it can reflect light most. That is, white light can reflect the light beam that has passed through the metal thin film layer most efficiently. Therefore, the laminated polyester film of the present invention preferably has a whiteness measured according to JIS Z-8722 from the surface layer (A) side of 75 or more, more preferably 80 or more. When the whiteness is less than 75, the complementary effect of reflecting the light transmitted through the metal thin film layer with the white light-shielding layer (B) tends to be reduced.

  In order to set the whiteness of the laminated polyester film to 75 or more, it is also effective to use a fluorescent whitening agent in addition to the means for improving the light shielding property described below. As means for improving the light shielding property, (1) a method of setting the void content of the white light shielding layer (B) to 10 to 50% by volume, (2) white inorganic particles in the white light shielding layer (B), and a white light shielding layer Examples thereof include a method of containing 1 to 25% by mass with respect to the resin composition of (B), (3) the combined use of both.

  In order to improve the light shielding property, a method of incorporating a large number of fine cavities inside the white light shielding layer (B) or a method of incorporating white inorganic particles is effective. The method of containing a large number of fine cavities is advantageous in that light-shielding properties are imparted and the laminated polyester film can be reduced in weight. Further, by using a fine cavity and white inorganic particles in combination, the light shielding property can be further enhanced. The white light-shielding layer (B) is more preferably an embodiment of either a fine void-containing polyester layer or a polyester layer containing white inorganic particles and fine voids from the viewpoint of light shielding properties and light weight.

  As the white inorganic particles, a white pigment made of titanium oxide, calcium carbonate, barium sulfate and a composite thereof is preferable. These white particles are preferably contained in an amount of 1 to 25% by mass with respect to the resin composition of the white light-shielding layer (B). If the content of inorganic particles is excessively increased to further improve the light shielding property, breakage may occur frequently during film production, and stable production at an industrial level may not be performed.

  As a method of containing a cavity in the white light-shielding layer (B), (1) a method of containing a foaming agent and foaming by heat during extrusion or film formation, or foaming by chemical decomposition, (2) extrusion A method of adding a gas such as carbon dioxide or a vaporizable substance at a time or after extrusion and foaming, (3) adding polyester and an incompatible thermoplastic resin to the polyester, and after melt extrusion, uniaxial or biaxial (4) A method in which organic or inorganic fine particles are added and melt-extruded and then uniaxially or biaxially stretched.

  Among the above-mentioned methods for containing cavities, the method of (3) above, that is, a method of adding a polyester and an incompatible thermoplastic resin to the polyester, and melt-extrusion and then stretching in a uniaxial or biaxial manner is preferable. . The thermoplastic resin incompatible with the polyester is not limited in any way, but is a polyolefin resin represented by polypropylene or polymethylpentene, a polystyrene resin, a polyacrylic resin, a polycarbonate resin, or a polysulfone resin. Resins, cellulose resins, polyphenylene ether resins and the like are exemplified.

  These thermoplastic resins incompatible with polyester may be used alone or in combination with a plurality of thermoplastic resins. The content of the thermoplastic resin incompatible with these polyesters is preferably 3 to 20% by mass, more preferably 5 to 15% by mass with respect to the resin forming the void-containing polyester layer (white light-shielding layer B). When the content of the thermoplastic resin incompatible with the polyester is less than 3% by mass with respect to the resin forming the void-containing polyester layer, the content of voids formed in the film is reduced, so that the light shielding property (hiding) ) Is reduced. Therefore, when the metal thin film layer is provided on the surface layer (A), the effect of reducing the variation in reflectance due to the thickness variation of the metal thin film layer tends to be insufficient. Further, the light weight characteristics are insufficient. On the other hand, when the content of the incompatible thermoplastic resin exceeds 20% by mass with respect to the resin forming the void-containing polyester layer (white light-shielding layer B), the frequency of breakage in the film manufacturing process increases. Tend. The void content in the white light-shielding layer (B) of the laminated polyester film of the present invention is preferably 10 to 50% by volume, more preferably 20 to 40% by volume.

  As described above, in the white light-shielding layer (B) used in the present invention, the method in which the method of blending the above polyester with an incompatible thermoplastic resin to form a cavity and the method of blending white particles are most preferable. .

The laminated polyester film of the present invention preferably has an apparent density of 0.60 to 1.35 g / cm ³ . The lower limit of the apparent density, in terms of handling property, more preferably 0.65 g / cm ^3, particularly preferably 0.70 g / cm ^3. The upper limit of the apparent density, in terms of weight reduction, more preferably 1.30 g / cm ^3, particularly preferably 1.20 g / cm ^3. When the apparent density is less than 0.60 g / cm ³ , since the void content is too high, the strength of the laminated polyester film is lowered, the waist is weakened, and the handleability is deteriorated. There is. On the other hand, when the apparent density exceeds 1.35 g / cm ³ , the content of voids inside the film is too low, and the effect of weight reduction becomes insufficient.

  In the present invention, the content of the voids in the white light-shielding layer (B), the type and content of the thermoplastic resin incompatible with the polyester, and the type and content of the inorganic particles are as described above. What is necessary is just to set suitably in the range indicated above by market requirements, such as the light transmittance of a polyester film, and an apparent density.

  In the laminated polyester film of the present invention, when the white light-shielding layer (B) contains cavities, a white polyester film that does not contain cavities caused by a thermoplastic resin incompatible with polyester, or a normal transparent polyester film In comparison with, the occurrence of curl curl is large. When the film is thick, curling is particularly likely to occur. Therefore, it is preferable to produce a film by using a method for suppressing curling.

  This is because in the production of a biaxially stretched film having a thick film, the unstretched film before stretching becomes very thick. Therefore, the cooling efficiency of the film by the cooling roll is different between the cooling surface and the opposite surface, and the structure such as the degree of crystallinity is different between the front and back of the film. Furthermore, since it is a void-containing polyester film containing fine cavities inside, the size, shape and volume fraction of the cavities easily change over the thickness direction of the film, so the physical properties and structure of the film front and back are the same. The production of such a film becomes extremely difficult.

  In the present invention, it is preferable that the curled value after heat-treating the laminated polyester film at 110 ° C. for 30 minutes in an unloaded state is 1 mm or less. The curl value is more preferably 0.9 mm or less, and further preferably 0.8 mm or less. When the curl value exceeds 1 mm, for example, handling properties during work under no tension when incorporated into a final product as a light reflecting plate or the like is not preferable.

  As a technique for suppressing curling, (1) a method for suppressing the occurrence of curling by resisting internal strain by reducing the volume fraction of the cavities and suppressing the size of each cavity, and (2) film (3) In order to control the curl caused by the structural difference between the front and back of the film applied in each step starting from the difference in crystallinity in the film thickness direction due to the cooling difference during extrusion. In addition, a method of positively generating a structural difference between the front and back of the film and complementing the necessary structural difference to bring the curl value close to zero is preferable.

  Specifically, the degree of orientation of the film front and back is controlled independently by setting the temperature or heat quantity of the film front and back to different values in the stretching process and heat setting process such as longitudinal stretching and lateral stretching, and the structure of the film front and back By adopting conditions that balance the physical properties, zero curl film formation is realized.

  In addition, as a basic requirement for stable production in a state where the curl is low over the entire width, it is also important to form cavities with little change in the film thickness direction by a stretching formulation with little thickness unevenness.

  More specifically, for the longitudinal curl immediately after film formation, the structural difference between the front and back of the film during longitudinal stretching is controlled, and the lateral curl controls the structural difference between the front and back of the film during lateral stretching and heat setting. Thus, a method of suppressing the curling by creating an internal strain in the opposite direction and balancing with the internal strain due to the structural difference between the front and back of the film, which is inevitably generated, is preferable.

  As another method for suppressing curling, the laminated polyester film is composed of at least three layers, and the thickness and composition of the surface layer (A) are set to the thickness of the surface layer (C) or the polyester layer (A ′). A method of making the compositions equivalent is also effective.

(Surface layer A)
In this invention, a surface layer (A) is a layer which forms the metal thin film layer used as a reflective surface, when using the laminated polyester film of this invention as a base material of a specular reflection film. This surface layer (A) is excellent in smoothness and is a layer having a function of increasing the reflectance when the metal thin film layer is formed.

  In the laminated polyester film of the present invention, the thickness of the surface layer (A) is preferably 5 to 30 μm. The upper limit of the thickness of the surface layer (A) is more preferably 25 μm, particularly preferably 20 μm. On the other hand, the lower limit of the thickness of the surface layer (A) is more preferably 7 μm, particularly preferably 10 μm. When the thickness of the surface layer (A) is less than 5 μm, the fine cavities and particles contained in the white light-shielding layer (B) may adversely affect the surface smoothness of the surface layer (A), which is not preferable. . On the other hand, when the thickness of the surface layer (A) exceeds 30 μm, the thickness of the white light-shielding layer (B) must be reduced while maintaining the light-shielding property, and the design of the white light-shielding layer (B) is described above. Thus, it may be necessary to change to a special prescription for thin concealment, and the operation becomes complicated.

  In the surface layer (A), it is important that the three-dimensional ten-point average roughness (SRz) is 0.23 μm or less. SRz is preferably 0.21 μm or less, more preferably 0.19 μm or less, and particularly preferably 0.16 μm or less.

  The higher the surface smoothness of the metal thin film layer, the higher the light reflectance. Therefore, it is preferable that the surface layer (A) is as excellent in surface smoothness as possible. When the three-dimensional ten-point average roughness (SRz) exceeds 0.23 μm, the light reflectance, particularly the regular reflectance, on the surface of the metal thin film layer when the metal thin film layer is formed decreases. For example, when such a specular reflection film with inferior regular reflectance is used as a surface light source reflector for LCD, the brightness of the display is lowered. In general, three-dimensional center plane average surface roughness (SRa) is often used as an index of surface smoothness. However, even if the surface has the same SRa, the surface morphology may be completely different, such as when there are a small number of high protrusions or when there are many low protrusions. In the present invention, it has been found that the higher protrusion among the surface protrusions has a greater influence on the light reflectance. In the present invention, for the reasons described above, three-dimensional ten-point average roughness (SRz) is used as an index of surface smoothness.

  The lower limit of SRz of the surface layer (A) is preferably as close to zero as possible from the viewpoint of light reflectance. However, in consideration of the extremely high level of technology required for surface smoothing at the extreme level and the measurement accuracy of the measuring device for detecting it, considering the practical light reflectance and stable productivity at the industrial level, A lower limit of SRz is sufficient to be 0.05 μm.

  In the present invention, the method for imparting the above properties is not limited, but it is a preferred embodiment that the surface layer (A) is substantially free of particles. “Substantially no particles” means, for example, in the case of inorganic particles, fluorescent X-rays using a calibration curve prepared in advance from analysis results obtained by other analysis methods such as atomic absorption spectrometry and emission spectrometry. It means a content that is 50 ppm or less, preferably 10 ppm or less, particularly preferably a detection limit or less when the element attributed to particles is quantified by an analytical method. This is because even if the particles are not actively included in the film, a very small amount of adhering matter, dirt, or foreign matter may be mixed during the production of the raw polymer or the film.

Furthermore, in the present invention, it is preferable that the number of protrusions present on the surface of the surface layer (A) having a height of 1 μm or more and a maximum diameter of 20 μm or more is 5 / m ² or less. It is more preferably 4 pieces / m ² or less, and further preferably 3 pieces / m ² or less. Projections having a height of 1 μm or more and a maximum diameter of 20 μm or more existing on the surface of the surface layer (A) are pinholes generated in the metal thin film layer when the metal thin film layer is formed on the surface layer (A). One of the causes. Therefore, when the number of protrusions exceeds 5 / m ² , when the metal thin film layer is formed on the surface layer (A), the frequency of occurrence of pin holes in the metal thin film layer increases, and this pin hole exists. In some cases, the reflected light is lowered at the location where the reflection occurs, and the entire reflected light becomes non-uniform.

In order to set the number of projections to 5 pieces / m ² or less, it is preferable not to positively contain particles in the polyester forming the surface layer (A). Furthermore, it is preferable to reduce foreign substances that cause pinholes in the metal thin film layer as much as possible. Foreign matter mixed in the surface layer (A) is a catalyst in the raw material polyester (polycondensation reaction catalyst, transesterification reaction catalyst), additive (electrostatic adhesion improver such as alkali metal salt / alkaline earth metal salt) And aggregates of heat stabilizers such as phosphoric acid or phosphate, and those resulting from these metal reduction products, contaminants mixed from the outside, high-melting-point organic materials, and the like. Further, dust adhering to the surface layer (A) during film production is also a cause of pinholes in the metal thin film layer.

  The polyester used in the present invention includes a polycondensation method in which a dicarboxylic acid and a glycol are esterified and then a polycondensation reaction, or a transesterification method in which a dicarboxylic acid salt and a glycol are transesterified and then a polycondensation reaction is performed. It is manufactured by a conventionally known method.

  In this polyester, a polycondensation catalyst, further a transesterification catalyst, and a thermal stabilizer such as phosphoric acid or phosphate are used as essential components. In addition to these, an appropriate amount of alkali metal salt or alkaline earth metal salt is contained, and by controlling the molar ratio of these metal salt and phosphorus atom, the sheet-like molten polyester is electrostatically applied onto a rotating cooling roll. Thus, an unstretched sheet having a uniform thickness can be stably obtained.

Typical polycondensation catalysts for polyester include Sb-based catalysts such as antimony trioxide and antimony glycolate, Ge-based catalysts, Ti-based catalysts, and Al-based catalysts. Of these, antimony trioxide (Sb ₂ O ₃ ) is generally used as a polycondensation catalyst for polyester for film from the viewpoints of transparency, thermal stability and cost.

In particular, when Sb ₂ O ₃ is used as a polycondensation catalyst, Sb ₂ O ₃ is reduced to metal Sb during polymerization and / or during production of an unstretched polyester film, and tends to precipitate as an aggregate on the film surface. Since this corresponds to the foreign matter (A), it is preferable to reduce the content of Sb ₂ O ₃ as much as possible within a range in which the polycondensation time is not significantly delayed. In order to make the number of deformed parts as described above within the above range, the content of Sb ₂ O _{3 in} the polyester is 50 to 250 ppm, preferably 60 to 200 ppm, more preferably 70 to 150 ppm in terms of metal Sb. It is recommended that

  After completion of the polycondensation, the polyester is filtered with a filter made of a filter material such as a sintered stainless steel having a pore size of 7 μm or less (initial filtration efficiency of 95%), or a melted polyester strand from an extruder for pelletization. When water is extruded into cooling water, the cooling water is filtered in advance (filter pore diameter: 1 μm or less), and this process is performed in a sealed room to reduce foreign substances of 1 μm or more present in the environment with a hepa filter. It is preferable to keep it.

  Further, when producing an unstretched polyester sheet, which will be described later, microfiltration is performed in order to remove foreign substances contained in the resin when the polyester is melted. The filter medium used for the microfiltration is not particularly limited, but the filter medium of the stainless steel sintered body is formed by reducing the polyester polymerization catalyst, such as metal Sb, Si, Ti mixed at the stage from polymerization to pelletization. , Ge and Cu are preferred because they are excellent in removing agglomerates and high melting point organic substances. The filterable particle size of the filter medium is preferably 15 μm or less (initial filtration efficiency 95%). When the particle size exceeds 15 μm, removal of particles having a size of 20 μm or more that needs to be removed may be insufficient. Although productivity may be lowered by performing microfiltration of a molten resin using a filter medium having the filtration performance as described above, it is extremely suitable for obtaining a film laminate having few optical defects.

  About dust adhering to the surface layer (A) at the time of film production, the adhesion of dust is reduced by producing a film in a clean environment in which foreign substances of 1 μm or more existing in the environment are reduced by using a hepa filter. be able to.

(Surface layer C)
In the present invention, the surface layer (C) is a layer having a function of imparting handling properties (sliding property, winding property, scratch resistance, etc.) to the laminated polyester film. When the laminated polyester film of the present invention has a two-layer structure of surface layer (A) / white light shielding layer (B), the white light shielding layer (B) also serves as the surface layer (C). In this case, the surface of the white light shielding layer (B) may be referred to as the surface C.

  When the laminated polyester film of the present invention is composed of three or more layers including the surface layer (A) / white light shielding layer (B) / surface layer (C), the thickness of the surface layer (C) is the handling property. There is no limitation in particular from the function of provision, For example, it shall be 5-30 micrometers. However, as with the surface layer (A), even when the thickness of the surface layer (C) is increased, the thickness of the white light-shielding layer (B) must be reduced while maintaining the light-shielding property. ) May have to be changed to a prescription for concealing thin objects as described above, and the operation becomes complicated.

  In the present invention, the three-dimensional ten-point average roughness (SRz) of the surface C or the surface layer (C) is preferably larger than SRz of the surface layer (A) and not more than 2.0 μm. The lower limit of SRz of the surface layer (C) is more preferably 0.25 μm, particularly preferably 0.27 μm. Even if SRz of surface C or surface layer (C) is larger than SRz of surface layer (A), if SRz of surface C or surface layer (C) is 0.23 μm or less, a laminated polyester film is wound. When taking, the slipperiness between the surface layer (A) and the surface C or the surface layer (C) deteriorates, for example, the production process of the laminated polyester film or the formation of the metal thin film layer In the processing step, the winding property of the laminated polyester film on a roll tends to be deteriorated. In addition, in the film manufacturing process and the film processing process, scratches occur on the surface of the smooth surface layer (A), and the light reflection characteristics on the surface of the metal thin film layer when the metal thin film layer is formed on the surface layer (A) are reduced. It becomes easy.

On the other hand, the upper limit of SRz of the surface C or the surface layer (C) is more preferably 1.8 μm, particularly preferably 1.6 μm. When SRz of the surface C or the surface layer (C) exceeds 2.0 μm, the effect of improving the handling property is saturated, and the phenomenon as described in the following (1) or (2) is likely to occur. When a metal thin film layer is formed on (A), the reflective properties of the metal thin film layer surface may be adversely affected.
(1) The surface layer (C) which contacts the surface C or the surface layer (C) when the protrusions on the surface C or the surface layer (C) are scraped off and fall off and the fallen material winds the laminated polyester film into a roll. Transfer to A).
(2) When the laminated polyester film is wound into a roll, the coarse protrusions on the surface C or the surface layer (C) make a mark on the surface layer (A), and the surface of the surface layer (A) becomes rough (hereinafter, It is abbreviated as engraving).

  When the laminated polyester film of the present invention is composed of two layers of surface layer (A) / white light shielding layer (B), the following method is used as a method for controlling SRz of surface C of white light shielding layer (B). Is preferred. For example, a method of adding inorganic particles such as calcium carbonate, barium sulfate, titanium oxide, silica and zeolite into the white light-shielding layer (B), a method of containing crosslinked organic particles such as acrylic, styrene and melamine, these particles The method of combining two or more is mentioned. This method is preferably used as an economical method in which the SRz of the surface C can be easily controlled.

  Further, in the present invention, when a void-containing film is used as the white light-shielding layer (B), the thermoplastic resin added as a void developing agent is dispersed in the polyester resin to contribute to the formation of surface irregularities. It is possible to control SRz by appropriately adjusting the addition amount of the cavity developing agent and the melt viscosity.

  In addition, when a particularly large SRz is required, the surface unevenness can be controlled also by subjecting one surface of the produced polyester film to a physical surface treatment such as mat processing. In addition, when performing the mat processing on the surface C of the white light-shielding layer (B), sufficient consideration is necessary so that the flatness of the film is not lost and minute foreign matters are not attached.

  Moreover, as a method for controlling SRz of the surface layer (C), a method of incorporating particles forming surface protrusions into the polyester forming the surface layer (C) is preferable. When the surface layer (C) is a single layer, the polyester constituting the surface layer (C) preferably contains 0.05 to 5 mass% of particles.

  In the present invention, the coefficient of static friction between the surface layer (A) of the laminated polyester film and the surface C or the surface layer (C) is preferably 0.60 or less, more preferably 0.55 or less, and particularly preferably. Is 0.50 or less. When the laminated polyester film has a layer structure of surface layer (A) / white light shielding layer (B) / polyester layer (A ′) / coating layer (C ′), the static friction coefficient is the surface layer. It means the coefficient of static friction between (A) and the coating layer (C ′).

  When the static friction coefficient exceeds 0.60, the same problem as when the surface C of the white light-shielding layer (B) or the three-dimensional ten-point average roughness (SRz) of the surface layer (C) is 0.23 μm or less. Is likely to occur. On the other hand, if the coefficient of static friction is too small, the effect of improving the handling property is reduced, and conversely, winding deviation is easily generated when winding in a roll shape. Therefore, the lower limit of the static friction coefficient is preferably 0.30, more preferably 0.35, and particularly preferably 0.40.

  In order to make the static friction coefficient 0.60 or less, it is effective to control the surface C of the white light-shielding layer (B) or SRz of the surface layer (C) to more than 0.23 μm and 2.0 μm or less. is there.

  In addition, in order to make the static friction coefficient 0.60 or less, in addition to the method of controlling the surface roughness with particles, for example, any one of the surface layer (A) and the surface layer (C) has a high grade. Examples thereof include a method of containing a lubricant comprising an ester derivative, an amide derivative or a metal salt of a fatty acid. Moreover, when the said laminated polyester film is comprised from 2 layers of a surface layer (A) / white light shielding layer (B), you may make the white light shielding layer (B) contain the said lubrication agent. In addition, when the surface layer (C) is composed of the coating layer (C ′), it is possible to use a method of improving slipperiness by adding a low-polarity surfactant to the coating layer (C ′). It is.

  The particles include calcium carbonate, kaolin, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, lithium fluoride, soju Inorganic particles such as um calcium aluminum silicate, organic salt particles such as terephthalate such as calcium oxalate, calcium, barium, zinc, manganese and magnesium, and vinyl of divinylbenzene, styrene, acrylic acid, methacrylic acid, acrylic acid or methacrylic acid Crosslinked polymer particles consisting of a single monomer or copolymer, polytetrafluoroethylene, benzoguanamine resin, thermosetting epoxy resin, unsaturated polyester, thermosetting urea resin, thermosetting phenol resin, etc. They include inert particles such as heat-resistant organic particles.

  The method of incorporating the particles in the polyester includes (a) a method of dispersing the particles in a slurry form in a diol which is a component of the polyester and adding the particle slurry to a polyester polymerization reaction system, and (b) a polyester film. (C) Method of kneading polyester and particles in a molten state (d) Melting the polyester and particle master resin with a vent type twin screw extruder A method of kneading in a state is exemplified.

  In the case of a method of adding to a polymerization reaction system, it is preferable to add a diol slurry of particles to a reaction system having a low melt viscosity before the esterification reaction or transesterification reaction and before the start of the polycondensation reaction. Moreover, when preparing the diol slurry of particles, it is preferable to perform a physical dispersion treatment such as a high-pressure disperser, a bead mill, or ultrasonic dispersion. Furthermore, in order to stabilize the dispersion-treated slurry, it is preferable to use an appropriate chemical dispersion stabilization treatment according to the type of particles used.

  For example, in the case of inorganic oxide particles or crosslinked polymer particles having a carboxyl group on the particle surface, an alkali compound such as sodium hydroxide, potassium hydroxide, or lithium hydroxide is added to the slurry. In addition, reaggregation between particles can be suppressed by electrical repulsion. In the case of calcium carbonate particles, hydroxyapatite particles, etc., it is preferable to add sodium tripolyphosphate or potassium tripolyphosphate to the slurry.

  In addition, when adding the diol slurry of particles to the polymerization reaction system of the polyester, the slurry can be heated to near the boiling point of the diol, or the heat shock (temperature difference between the slurry and the polymerization reaction system) when added to the polymerization reaction system. ) Can be reduced, which is preferable in terms of dispersibility of the particles.

  As another layer configuration for controlling SRz of the outermost layer on the opposite side of the surface layer (A), the surface layer (A) / white light shielding layer (B) / polyester layer (A ′) / coating layer (C ′) It can also be set as the laminated structure which consists of these layer structures. For the polyester layer (A ′), as in the surface layer (A), a polyester containing substantially no particles or a polyester having a particle content of less than 100 ppm is used. Further, a coating layer (C ′) made of a resin composition containing particles is laminated on the polyester layer (A ′), the coating layer (C ′) is the outermost layer, and the surface opposite to the surface layer (A) is formed. It is a method of roughening. Moreover, the co-extrusion process at the time of manufacturing a laminated polyester film can be simplified with A / M / A (A ') by using the same raw material as a surface layer (A) as a raw material of a polyester layer (A'). There are advantages and more preferred embodiments.

When the laminated polyester film has a laminated structure consisting of surface layer (A) / white light shielding layer (B) / polyester layer (A ′) / coating layer (C ′), the laminated portion of A / B / A ′ is biaxial. A method comprising a stretched film, in which the coating layer (C ′) is laminated by the coating layer and the coating amount after the final drying is 0.01 to 0.5 g / m ² is suitable. Further, a method is used in which a polyester layer containing polyester and particles and having a thickness of 0.1 to 3 μm is laminated on the polyester layer (A ′) by coextrusion without forming the coating layer (C ′). You can also

  In the production process of the laminated polyester film, the coating layer (C ′) is applied to an unstretched film or a uniaxially stretched film with a coating layer (C ′) coating solution containing resin and particles, dried, and then at least unidirectional. A method of forming by a so-called in-line coating method in which a coating layer (C ′) is formed by stretching and heat-treating is preferable from the viewpoint of film characteristics (sliding property, blocking property, transparency, etc.) and economical efficiency. A typical production example of a laminated polyester film composed of surface layer A / white light shielding layer B / polyester layer (A ′) / coating layer (C ′) is shown below. In the following production examples, the same raw material as the surface layer (A) was used as the raw material for the polyester layer A ′.

  Using two extruders, a laminated polyester film composed of two types and three layers in which the layer (A) is laminated on both sides of the white light-shielding layer (B) is used as a rotating cooling metal roll using a co-extrusion die. It is melt-extruded into a sheet and cooled and solidified by an electrostatic application method to obtain an unstretched polyester sheet. The obtained unstretched polyester sheet is stretched 2.5 to 5.0 times in the longitudinal direction with, for example, a roll heated to 80 to 120 ° C. to obtain a uniaxially stretched film. Furthermore, the edge part of a film is hold | gripped with a clip, for example, it guide | induced to the hot air zone heated at 70-140 degreeC, and is extended | stretched 2.5 to 5.0 times in the width direction after drying. Subsequently, it is guided to a heat treatment zone at 160 to 240 ° C., and heat treatment is carried out for 1 to 60 seconds to complete crystal orientation and obtain a laminated polyester film. At any stage in the film production process, particularly preferably at the stage of a uniaxially stretched film, a coating solution for forming the coating layer (C ′) is applied to one side of the laminated polyester film, and the coating layer (C ′) Is laminated.

  In the present invention, the coating layer (C ′) is preferably composed of a resin composition containing particles a having an average particle size of 20 nm or more and less than 150 nm and particles b having an average particle size of 150 nm or more and 600 nm or less.

  Examples of such particles include (1) calcium carbonate, calcium phosphate, silica, silica-alumina composite oxide particles, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, etc. Inorganic particles, (2) crosslinked polymer particles such as crosslinked polystyrene, crosslinked polymethyl methacrylate, and crosslinked acryl, (3) heat-resistant polymer particles such as silicon resin particles, polyimide particles, and fluorine resin particles, (4 ) Organic particles such as calcium oxalate can be mentioned. Of these, silica particles are most preferred because of their good affinity with polyester.

  In the present invention, it is preferable to contain two types of particles (particle a and particle b) having different average particle diameters. The average particle size of the particles a is preferably 20 nm or more and less than 150 nm, and more preferably 30 to 100 nm. When the average particle size of the particles a is less than 20 nm, the slipping property is insufficient. On the other hand, when the average particle size of the particles a is 150 nm or more, the scratch resistance tends to deteriorate.

  In the present invention, in order to improve the balance between slipperiness, scratch resistance, and engraving properties, it is preferable to use particles b having a larger average particle size than particles a in addition to particles a. The average particle diameter of the particles b is preferably 150 to 600 nm, more preferably 200 to 500 nm. If the average particle size of the particles b is less than 150 nm, the slipping property and the scratch resistance tend to deteriorate. On the other hand, if the average particle size of the particles b exceeds 600 nm, the wear resistance tends to deteriorate and the stampability tends to deteriorate.

  Furthermore, the difference in the average particle diameter between the particles b and the particles a is preferably 100 nm or more, and particularly preferably 150 nm or more, which is more effective in terms of the balance of slipperiness, scratch resistance, and stampability.

  In the present invention, the three-dimensional ten-point average roughness (SRz) of the coating layer (C ′) is preferably in the same range as the surface layer (C) in the case of the single layer configuration.

  In order to set the three-dimensional ten-point average roughness (SRz) of the coating layer (C ′) in the same range as that of the surface layer (C) in the case of the single layer configuration, the average particle diameter of the coating layer is 20 nm. The mass ratio (a / b) of the particles a having a particle diameter of 150 nm to less than 150 nm and the particles b having an average particle diameter of 150 nm to 600 nm is set to 3 to 30, and the content of the particles B is set to 0. 0 relative to the resin composition of the coating layer. It is preferable to set it as 1-3 mass%. In particular, when the content of the particles b exceeds 3% by mass with respect to the resin composition of the coating layer, the scratch resistance tends to be significantly reduced. Here, the resin composition of a coating layer means the sum total of solid content mass of resin, particle | grains a, and particle | grains b.

  In the present invention, the coating liquid used for forming the coating layer is mainly composed of a solvent, a resin, and particles. As the solvent, either an aqueous solvent or an organic solvent can be used, but an aqueous solvent is preferable from the viewpoint of working environment, environmental protection, productivity, and the like.

The water-soluble or water-dispersible resin used for the coating layer (C ′) in the present invention is preferably a resin comprising any of the following (i) to (iii).
(I) A graft copolymer of an aromatic polyester containing 5% by mass or more of a radical polymer composed of at least one monomer containing an acid anhydride having a double bond (ii) An acid value of 200 eq / t or more Acrylic resin or its copolymer (excluding (iii))
(Iii) A copolymer of an acrylic resin having an acid value of 200 eq / t or more, containing 5% by mass or more of a radical polymer comprising at least one monomer containing an acid anhydride having a double bond

  The aromatic polyester resin refers to a resin containing 30 mol% or more of an aromatic dicarboxylic acid component in the acid component of polyester. If the aromatic dicarboxylic acid component is less than 30 mol%, the hydrolyzability of the polyester becomes remarkable and the water resistance tends to deteriorate.

  The acid value in the acrylic resin is a value obtained by titrating a solid content after drying a resin solution or the like at 80 ° C. under a reduced pressure of 100 Pa for 2 hours with an ethanolic potassium hydroxide solution having a known concentration. It is.

  If the acid value of the acrylic resin is less than 200 eq / t, the dispersibility in an aqueous solvent may be lowered, which is not preferable.

  In order to make the acid value 200 eq / t or more, it is necessary to contain a polar group in the molecule. However, a stable polar group that does not change even when heated, such as sodium sulfonate, is not preferable because it deteriorates the water resistance of the coating layer.

  Examples of the polar group that does not deteriorate the water resistance of the coating layer include amine salts of carboxylic acids that decompose after heating and have a reduced polarity. The amine that can be used is preferably vaporized under the drying conditions of the coating film, and examples thereof include ammonium, diethylamine, and triethylamine.

  More preferably, at least one resin selected from an aromatic polyester resin or an acrylic resin having an acid value of 200 eq / t or more, or two or more copolymers contains an acid anhydride having a double bond. It is to contain 5% by mass or more of a radical polymer composed of at least one monomer. If it is less than 5% by mass, the effect of water resistance tends to be insufficient.

  By introducing the acid anhydride into the resin, a crosslinking reaction can be performed between the resin molecules. That is, the acid anhydride in the resin is converted to carboxylic acid by hydrolysis in the coating solution, and reacts with the acid anhydride or active hydrogen groups of other molecules between molecules due to thermal history during drying and film formation. Thus, ester groups and the like can be generated, and the resin of the coating layer can be cross-linked to exhibit water resistance and heat whitening prevention property.

  Examples of the monomer containing an acid anhydride having a double bond include maleic anhydride, itaconic anhydride, 2,5-norbornene dicarboxylic acid, and tetrahydrophthalic anhydride. The radical polymer may be a copolymer with another polymerizable unsaturated monomer.

  Other polymerizable unsaturated monomers include: (1) fumaric acid, monoethyl fumarate, diethyl fumarate, monoester or diester of fumaric acid such as dibutyl fumarate, (2) maleic acid, monoethyl maleate, malee Monoester or diester of maleic acid such as diethyl acid, dibutyl maleate, (3) itaconic acid, monoester or diester of itaconic acid, (4) maleimide such as phenylmaleimide, (5) styrene, α-methylstyrene, Styrene derivatives such as t-butylstyrene and chloromethylstyrene, (6) vinyltoluene, divinylbenzene, etc. (7) alkyl acrylate, alkyl methacrylate (the alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl group, isobutyl group, t- (8) 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl, and the like. (8) 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl, acryl group, 2-ethylhexyl group, cyclohexyl group, phenyl group, benzyl group, phenylethyl group Acrylate, hydroxy-containing acrylic monomer of 2-hydroxypropyl methacrylate, (9) acrylamide, methacrylamide, N-methyl methacrylamide, N-methyl acrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-di Methylolacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, amide group-containing acrylic monomer of N-phenylacrylamide, (10) N, N-diethylaminoethyl acrylate Amino group-containing acrylic monomer of N, N-diethylaminoethyl methacrylate, (11) glycidyl acrylate, epoxy group-containing acrylic monomer of glycidyl methacrylate, (12) acrylic acid, methacrylic acid, and salts thereof (sodium salt) , Potassium salts, ammonium salts), and the like, and acrylic monomers containing a carboxyl group or a salt thereof.

  Moreover, in order to further improve the water resistance of the coating layer, it is particularly preferable to add an acid compound when adjusting the coating solution. By adding this acid compound, the acid anhydride and esterification reaction of the carboxylic acid group in the resin can be promoted and the crosslinking of the resin can be improved.

  The addition amount of the acid compound is preferably in the range of 1 to 10% by mass with respect to the resin. Although various compounds can be used as the acid compound, a low-boiling point carboxylic acid that is easily vaporized by heat during film formation, has a small residual amount in the coating layer, and has a small adverse effect at the time of residual is low. preferable. Examples of the low boiling point carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, heptanoic acid and the like.

  In the present invention, when performing a crosslinking reaction using the acid anhydride, it is possible to use a crosslinking agent that does not contain a nitrogen atom or phenols, which suppresses water resistance and discoloration during recovery and reuse. To preferred.

  Examples of the crosslinking agent containing no nitrogen atom or phenol include, for example, orthophthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, p-oxybenzoic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, Hexahydrophthalic acid diglycidyl ester, succinic acid diglycidyl ester, adipic acid diglycidyl ester, sebacic acid diglycidyl ester, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1, 6-hexanediol diglycidyl ether and polyalkylene glycol diglycidyl ether, trimellitic acid triglycidyl ester, 1,4-diglycidyl Oxybenzene, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol triglycidyl ether, triglycidyl ether of glycerol alkylene oxide adducts, include multifunctional epoxy compounds such as.

  A crosslinking agent containing a nitrogen atom or a phenol is oxidized and decomposed by heat or the like to produce a compound having a conjugated structure centered on a nitrogen atom and an aromatic ring. As a result, coloring becomes remarkable. However, in the present invention, the use of these cross-linking agents is not completely denied, and the cross-linking agents (curing resins) can be used as long as they are within a range where excellent water resistance and discoloration during recovery and reuse can be suppressed. ) Can be used in an appropriate amount depending on the type.

  Examples of the crosslinking agent containing a nitrogen atom include (1) an adduct of urea, melamine, benzoguanamine and the like with formaldehyde, and (2) an alkyl ether compound comprising these adduct and an alcohol having 1 to 6 carbon atoms. (3) a polyfunctional epoxy compound containing a nitrogen atom, (4) a polyfunctional isocyanate compound, (5) a blocked isocyanate compound, (6) a polyfunctional aziridine compound, (7) an oxazoline compound, etc. Can be mentioned.

  Examples of the amino resin described in (2) include methoxylated methylol urea, methoxylated methylol N, N-ethylene urea, methoxylated methylol dicyandiamide, methoxylated methylol melamine, methoxylated methylol benzoguanamine, butoxylated methylol melamine, butoxylated. Examples include methylol benzoguanamine. Among these, methoxylated methylol melamine, butoxylated methylol melamine, methylolated benzoguanamine, and the like are preferable.

  Examples of the polyfunctional epoxy compound containing a nitrogen atom described in (3) include triglycidyl isocyanurate, diglycidyl propylene urea, and the like.

  Examples of the polyfunctional isocyanate compound described in (4) include low-molecular or high-molecular aromatic, aliphatic diisocyanates, and trivalent or higher polyisocyanates.

  Examples of polyisocyanates include tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and trimers of these isocyanate compounds. The

  Further, an excess amount of these isocyanate compounds and low molecular active hydrogen compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, or polyester polyols, poly Examples thereof include terminal isocyanate group-containing compounds obtained by reacting polymer active hydrogen compounds such as ether polyols and polyamides.

  The blocked isocyanate described in (5) can be synthesized by subjecting the isocyanate compound and a blocking agent to an addition reaction by a known method.

  Examples of the isocyanate compound blocking agent include (a) phenols such as phenol, cresol, xylenol, resorcinol, nitrophenol and chlorophenol, (b) thiophenols such as thiophenol and methylthiophenol, and (c) acetoxime. Oximes such as methyl etiketooxime and cyclohexanone oxime, (d) alcohols such as methanol, ethanol, propanol and butanol, (e) halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol (F) Tertiary alcohols such as t-butanol and t-pentanol, (g) Lactams such as ε-caprolactam, δ-valerolactam, ν-butyrolactam, β-propyllactam, (h) aroma Tribe Mines, (i) Imides, (j) Active methylene compounds such as acetylacetone, acetoacetate, ethyl malonate, (k) mercaptans, (l) imines, (m), ureas, (n) And diaryl compounds, (o) sodium bisulfite, and the like.

  Examples of the crosslinking agent containing phenols include phenol formaldehyde resins and polyfunctional epoxy compounds containing bisphenol A, which are condensates with formaldehyde such as alkylated phenols and cresols.

  Examples of the phenol formaldehyde resin include alkylated (methyl, ethyl, propyl, isopropyl or butyl) phenol, p-ter-amylphenol, 4,4′-sec-butylidenephenol, p-ter-butylphenol, o-cresol. , M-cresol, p-cresol, p-cyclohexylphenol, 4,4'-isopropylidenephenol, p-nonylphenol, p-octylphenol, 3-pentadecylphenol, phenol, phenyl o-cresol, p-phenylphenol, xylenol And a condensate of phenols with formaldehyde.

  A polyfunctional epoxy compound is mentioned as a crosslinking agent which does not contain a nitrogen atom or phenols. However, since polyfunctional epoxy compounds often use amine-based crosslinking catalysts containing nitrogen atoms, there is a problem that coloring due to the catalyst occurs. Further, although it is possible to suppress coloring by reducing the amount of catalyst or using a catalyst that does not contain an amine or the like, it is preferable because crosslinking is insufficient or a gel-like mixture increases at the time of recovery. Absent.

  Examples of the polyfunctional epoxy compound described above include diglycidyl ether of bisphenol A and oligomers thereof, diglycidyl ether of hydrogenated bisphenol A and oligomers thereof, orthophthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, and terephthalic acid diester. Glycidyl ester, p-oxybenzoic acid diglycidyl ester, tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, succinic acid diglycidyl ester, adipic acid diglycidyl ester, sebacic acid diglycidyl ester, ethylene glycol diglycidyl ester Ether, propylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether And polyalkylene glycol diglycidyl ethers, trimellitic acid triglycidyl ester, triglycidyl isocyanurate, 1,4-diglycidyloxybenzene, diglycidyl propylene urea, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tri And glycidyl ether, triglycidyl ether of glycerol alkylene oxide adduct, and the like.

  As catalysts for polyfunctional epoxy compounds, quaternary ammonium salts such as triethylbenzylammonium chloride and tetramethylammonium chloride, tertiary amines such as benzyldimethylamine, tributylamine and tris (dimethylamino) methylphenol, 2-methyl-4- Imidazole compounds such as ethyl imidazole and 2-methylimidazole, nitrogen-containing heterocyclic compounds such as pyridine and methylpyridine, and catalysts not containing amines include strong bases such as sodium hydroxide and potassium hydroxide, borofluorination Examples thereof include metal compounds such as zinc and tin tetrachloride.

  In addition, when the coating layer is formed using an aqueous coating solution, an anionic coating is used to improve the wettability to the substrate film and coat the coating solution uniformly when coating on the surface of the substrate film. It is preferable to add an appropriate amount of a surfactant or a nonionic surfactant to the coating solution.

  In the coating solution, a plurality of other resins may be added to the coating solution in order to improve performance. Further, in the coating solution, inorganic and / or organic particles, antistatic agent, ultraviolet absorber, organic lubricant, in order to impart other functions such as handling property, antistatic property and antibacterial property to the film, Additives such as antibacterial agents and photo-oxidation catalysts can be included.

  When an aqueous solvent is used as a solvent used in the coating solution, alcohols such as ethanol, isopropyl alcohol, and benzyl alcohol may be mixed in a range of less than 50% by mass with respect to the entire coating solution. Furthermore, if it is less than 10 mass%, you may mix in the range which can melt | dissolve organic solvents other than alcohol. However, the total amount of alcohols and other organic solvents in the coating solution is preferably less than 50% by mass.

  If the addition amount of the organic solvent is less than 50% by mass, the drying property is improved during coating and drying, and the appearance of the coating layer is improved as compared with the case of water alone. If the amount is 50% by mass or more, the evaporation rate of the solvent increases, so that the concentration change of the coating solution occurs during coating, the viscosity of the coating solution increases and the coating property decreases. As a result, the appearance defect of the coating layer tends to occur. Furthermore, it is not preferable from the viewpoints of the environment, the health of workers, and the risk of fire.

  Furthermore, removal of foreign matters in the coating solution is effective for improving the scratch resistance and the stamping property of the coating layer (C ′).

  The filter medium for microfiltration of the coating solution preferably has a filtration particle size (initial filtration efficiency: 95%) of 25 μm or less. When the filtration particle size exceeds 25 μm, removal of coarse aggregates tends to be insufficient. Therefore, coarse agglomerates that could not be removed by filtration spread due to stretching stress in the uniaxial stretching or biaxial stretching process after coating and drying, causing a defect as aggregates of 100 μm or more.

  There is no particular limitation on the type of filter medium for finely filtering the coating solution as long as it has the above performance, and examples thereof include a filament type, a felt type, and a mesh type. The material of the filter medium for finely filtering the coating solution is not particularly limited as long as it has the above performance and does not adversely affect the coating solution, and examples thereof include stainless steel, polyethylene, polypropylene, and nylon.

  The coating solution can be applied by any known method. For example, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, air knife coating method, wire barber coating method, pipe doctor method, impregnation / coating method and curtain coating method. These methods can be used alone or in combination.

  The coating layer (C ′) may be obtained by applying the coating solution to a biaxially stretched polyester film substrate (offline coating method), or applying the coating solution to an unstretched or uniaxially stretched polyester film substrate. After coating, drying, and further uniaxial stretching or biaxial stretching may be performed, followed by heat setting (inline coating method), but the latter inline coating method is preferred from the viewpoint of performance and economy. The film coated with the coating solution can be led to a tenter for stretching and heat setting, and heated there to form a stable film by a thermal crosslinking reaction.

  In the case of the so-called in-line coating method, after applying the above coating liquid to an unstretched or uniaxially stretched polyester film substrate, drying and stretching, in the drying process after coating, only the solvent component such as water is removed, and the coating layer It is preferable to select a temperature and a time at which the crosslinking reaction does not proceed.

  The drying temperature is preferably 70 to 140 ° C., and the drying time is adjusted according to the solid content concentration and the coating amount of the coating solution, but the product of temperature (° C.) and time (seconds) is 3,000 or less. It is preferable. When the product exceeds 3,000, the coating layer undergoes a crosslinking reaction before stretching, and cracks and the like are likely to occur in the coating layer.

  Moreover, after extending | stretching a coating layer, in the state which fixed the film so that film width length does not change, it is bridge | crosslinking by heat-processing a coating layer for a short time of 0.5 to 1 second at 250-260 degreeC with an infrared heater. It is preferable for promoting the reaction.

  Under the present circumstances, when 1-10 mass% of acid compounds are added with respect to resin in the coating liquid, a crosslinking reaction will be further accelerated | stimulated and a coating layer will become firmer. Therefore, the oligomer which precipitates on the film surface when the film is heated can be blocked by the coating layer, and oligomer deposition on the surface of the coating layer can be suppressed.

  The stretched film is usually subjected to a relaxation treatment of about 2 to 10%, but in the present invention, the coating layer is coated with an infrared heater in a state where the coating layer is less distorted, that is, in a state where the film width is not changed. It is preferable to heat. By adopting such a method, crosslinking in the coating layer is promoted and becomes stronger. If the heating temperature or time is greater than the above conditions, crystallization or dissolution of the film tends to occur. On the other hand, if the one condition is lower than the heating temperature or time, crosslinking of the coating layer tends to be insufficient.

The coating amount after drying of the coating layer on the surface of the finally obtained coating film (solid content mass per unit film area) is preferably 0.01 to 0.50 g / m ² , more preferably 0.02 to 0.00. a 40 g / m ^2, particularly preferably 0.05~0.30g / m ^2. When the coating amount after drying is less than 0.01 g / m ² , the adhesiveness is insufficient. When the coating amount exceeds 0.50 g / m ² , it tends to be easily blocked, and the number of foreign matters in the coating layer is also likely to increase.

In addition, it is attached to the film surface that the cleanness in the air in the coating process (number of particles of 0.5 μm or more / ft ³ ) is controlled by a hepafilter so as to be class 100,000 after the unstretched film is formed. It is effective in reducing foreign matter.

(Polyester oligomer reduction treatment)
When the laminated polyester film of the present invention is heat-treated at 170 ° C. for 20 minutes, the laminated polyester film is deposited on the surface opposite to the smooth surface layer (A) (hereinafter sometimes referred to as “surface C”). it is preferable to filling ratio of the particles is controlled to 0.008μm ² / μm ² or less. Filling ratio of particles deposited on the surface of the surface layer (B) after the heat treatment of said more preferably 0.004 m ² / [mu] m ² or less, more preferably 0.002μm ² / μm ² or less, particularly preferably Is 0.001 μm ² / μm ² or less. After heat treatment described above, when the filling ratio of particles deposited on the surface C is more than 0.008μm ² / μm ^2, due particulate cyclic trimer precipitated on the film surface, the drawback to the metal thin film layer May occur. Further, when the precipitate is transferred to the surface of the metal thin film layer at the time of winding the film, the light reflectance on the surface of the metal thin film layer may be lowered.

  In a specular reflection film in which a metal thin film layer is laminated on a laminated polyester film, anchor treatment for improving the adhesion between the laminated polyester film and the metal thin film layer is widely performed before the metal thin film layer is formed. Therefore, the deposits present on the surface of the metal thin film layer, that is, the surface of the smooth surface layer (A) in the laminated polyester film of the present invention are suppressed by the formation of this undercoat layer, rather than the metal thin film layer. It is important to suppress precipitates on the surface C on the opposite side of the surface layer (A) that forms the film.

  The particles deposited on the film surface are low molecular weight substances mainly composed of low-polymerization oligomers and monomers such as cyclic trimers, and conventionally, the polyester film surface is washed or eluted with a solvent that dissolves the deposited particles, It has been quantified by quantifying a cyclic trimer or the like dissolved in a solvent. Therefore, as described above, the method extracts not only the film surface but also the oligomers present in the film, so that the correspondence with the practical characteristics is not good.

  Therefore, the present inventors paid attention to the fact that surface precipitates exist as particles, and found that the area occupied by these precipitated particles deposited on the surface by a microscope can be quantified. That is, the present inventors have found that the surface of a laminated polyester film that has been heat-treated under the conditions assuming the heat received by the laminated polyester film in the metal thin film layer forming step can be evaluated by a surface analysis method using an interference microscope. Thereby, the surface contamination caused by the surface migration of oligomers such as a cyclic trimer contained in the polyester film generated in the processing step of forming the metal thin film layer described above can be evaluated in a model manner.

In the present invention, for the surface of the smooth surface layer (A), more be occupied area ratio of particles deposited upon heating treatment at 170 ° C. 20 minutes to control the 0.008μm ² / μm ² or less preferable. As a result, the occurrence of defects in the metal thin film layer due to the precipitated particles is suppressed.

  In the present invention, the method for reducing the above-mentioned precipitated particles (low molecular weight products mainly composed of low-polymerization oligomers and monomers such as cyclic trimers) to a specific range is not limited. For example, the method of reducing the amount of cyclic trimers contained in the polyester constituting the laminated polyester film can be mentioned.

  When reducing the amount of the cyclic trimer in the polyester, the total amount of the cyclic trimer in the polyester is preferably 8000 ppm or less. 6000 ppm or less is more preferable, and 4000 ppm or less is more preferable. If it exceeds 8000 ppm, the effect of suppressing surface precipitation particles will be reduced.

  In the present invention, the polyester used as a raw material for the laminated polyester film is a polycondensation method in which a dicarboxylic acid and a glycol are esterified and then a polycondensation reaction, or a dicarboxylic acid salt and a glycol are transesterified and then polycondensed. It is produced by a conventionally known method such as a transesterification method for carrying out the reaction.

  In this polyester, a polycondensation catalyst, further a transesterification catalyst, and a thermal stabilizer such as phosphoric acid or phosphate are used as essential components. In addition to these, an appropriate amount of alkali metal salt or alkaline earth metal salt is contained, and by controlling the molar ratio of these metal salt and phosphorus atom, the sheet-like molten polyester is electrostatically applied onto a rotating cooling roll. Thus, an unstretched sheet having a uniform thickness can be stably obtained.

Typical polycondensation catalysts for polyester include Sb-based catalysts such as antimony trioxide and antimony glycolate, Ge-based catalysts, and Ti-based catalysts. Of these, antimony trioxide (Sb ₂ O ₃ ) is generally used as a polycondensation catalyst for polyester for film from the viewpoints of transparency, thermal stability and cost.

In particular, when Sb ₂ O ₃ is used as a polycondensation catalyst, Sb ₂ O ₃ is reduced to metal Sb during polymerization and / or during production of an unstretched polyester film, and tends to precipitate as an aggregate on the film surface. Since this corresponds to the foreign matter (A), it is preferable to reduce the content of Sb ₂ O ₃ as much as possible within a range in which the polycondensation time is not significantly delayed. In order to make the number of deformed parts as described above within the above range, the content of Sb ₂ O _{3 in} the polyester is 50 to 250 ppm, preferably 60 to 200 ppm, more preferably 70 to 150 ppm in terms of metal Sb. It is recommended that

  After completion of the polycondensation, the polyester is filtered with a filter made of a filter material such as a sintered stainless steel having a pore size of 7 μm or less (initial filtration efficiency of 95%), or a melted polyester strand from an extruder for pelletization. When water is extruded into cooling water, the cooling water is filtered in advance (filter pore diameter: 1 μm or less), and this process is performed in a sealed room to reduce foreign substances of 1 μm or more present in the environment with a hepa filter. It is preferable to keep it.

  Further, when producing an unstretched polyester sheet, microfiltration is performed to remove foreign substances contained in the polyester when the polyester is melted. The filter medium used for the microfiltration is not particularly limited, but the filter medium of the stainless steel sintered body is formed by reducing the polyester polymerization catalyst, such as metal Sb, Si, Ti mixed at the stage from polymerization to pelletization. , Ge and Cu are preferred because they are excellent in removing agglomerates and high melting point organic substances. The filterable particle size of the filter medium is preferably 15 μm or less (initial filtration efficiency 95%). When the filterable particle size of the filter medium exceeds 15 μm, removal of particles having a size of 20 μm or more to be removed may be insufficient. Although productivity may be reduced by performing microfiltration of a molten resin using a filter medium having the filtration performance as described above, it is extremely suitable for obtaining a laminated polyester film with few optical defects.

  The method for producing the polyester having a reduced content of the cyclic trimer (hereinafter referred to as low oligomer-treated polyester) is not limited, but a melt-polymerized polyester prepolymer having an intrinsic viscosity of 0.40 to 0.60 dl / g. And a method of subjecting polyester having a predetermined intrinsic viscosity to a heat treatment under an inert gas atmosphere or under reduced pressure under conditions where the intrinsic viscosity does not substantially change. Furthermore, there is a method of extracting with a solvent that dissolves the cyclic trimer.

  In order to suppress particles precipitated on the film surface, the total amount of polyester forming the surface layer may be low oligomer-treated polyester, or a mixture of low oligomer-treated polyester and general-purpose polyester may be used.

  In addition, since the cyclic trimer is produced in the melt extrusion process during the production of the polyester film, a method of reducing the increase in the cyclic trimer to 5000 ppm or less when the polyester is melted at a temperature of 290 ° C. for 30 minutes. It may be adopted. The increase amount of the cyclic trimer is preferably 3000 ppm or less, more preferably 2000 ppm or less, and particularly preferably 1000 ppm.

  Moreover, the method of reducing the increase amount of the cyclic trimer to 5000 ppm or less when melted at a temperature of 290 ° C. for 30 minutes is shown below. In order to suppress the regeneration of the cyclic trimer in the molten state at the time of molding as much as possible, it is important to reduce the amount of the active polymerization catalyst remaining in the polyester as much as possible. As a typical means for reducing the amount of such an active polymerization catalyst, the following method may be mentioned.

  One method includes a method of inactivating the polymerization catalyst by contacting polyester with water.

  Examples of the method for deactivating the polyester polycondensation catalyst include a method in which the polyester chip is contacted with water, water vapor or water vapor-containing gas after melt polycondensation or after solid phase polymerization.

  Examples of the water treatment method include a method of immersing in water and a method of applying water on the chip with a shower. The treatment time is 5 minutes to 2 days, preferably 10 minutes to 1 day, more preferably 30 minutes to 10 hours, and the water temperature is 20 to 180 ° C., preferably 40 to 150 ° C., more preferably 50 to 120 ° C.

  Although the method of performing water treatment industrially is illustrated below, it is not limited to this. The treatment method may be either a continuous method or a batch method, but the continuous method is preferred for industrial use.

  A silo-type treatment tank is used when water-treating polyester chips in a batch system. In other words, the polyester chip is received in a silo and treated with water in a batch system. In the case where the polyester chips are water-treated in a continuous manner, the polyester chips can be continuously or intermittently received in the tower-type treatment tank from the upper part and water-treated.

  When the polyester chip and water vapor or water vapor-containing gas are contacted, the water vapor or water vapor containing gas or water vapor containing air at a temperature of 50 to 150 ° C., preferably 50 to 110 ° C., is preferably granular polyethylene terephthalate. -0.5 g or more of water vapor is supplied per 1 kg of tort or brought into contact with granular polyethylene terephthalate and water vapor.

  The contact between the polyester chip and water vapor is usually performed for 10 minutes to 2 days, preferably 20 minutes to 10 hours.

  Hereinafter, a method for industrially performing the contact treatment between the granular polyethylene terephthalate and the water vapor or the water-containing gas is exemplified, but the method is not limited thereto. The processing method may be either a continuous method or a batch method.

  When a polyester chip is contact-treated with water vapor in a batch system, a silo type processing apparatus can be used. That is, a polyester chip is received in a silo, and contact processing is performed by supplying steam or a steam-containing gas in a batch manner.

  In the case where polyester chips are continuously contacted with water vapor, a granular polyethylene terephthalate is continuously received from the top in a tower-type processing apparatus, and water vapor is continuously supplied in parallel flow or countercurrent to be contacted with water vapor. Can do.

  As described above, when treated with water or steam, the granular polyethylene terephthalate is drained with a draining device such as a vibrating sieve or a Simon Carter as necessary, and transferred to the next drying step by a conveyor.

  For drying the polyester chip that has been contact-treated with water or water vapor, a commonly used polyester drying treatment can be used. As a continuous drying method, a hopper-type ventilation dryer is generally used in which a polyester chip is supplied from the upper part and a drying gas is supplied from the lower part.

  As a dryer for drying in a batch mode, drying may be performed while aeration gas is passed under atmospheric pressure.

  As the dry gas, atmospheric air may be used, but dry nitrogen and dehumidified air are preferable from the viewpoint of preventing molecular weight reduction due to hydrolysis or thermal oxidative decomposition of polyester.

  In addition, in the case of an aluminum or titanium-based polycondensation catalyst having a small effect by the above method, a method in which a phosphorus compound is added to a melt of a polyester after melt polycondensation or after solid-phase polymerization and the polymerization catalyst is inactivated. It is done.

  In the case of melt-polymerized polyester, there is a method of inactivating the aluminum catalyst by mixing the polyester after completion of the melt-polymerization reaction and the polyester compounded with the phosphorus compound in a device such as a line mixer that can be mixed in a molten state. Can be mentioned.

  In addition, as a method of blending the phosphorus compound with the solid phase polymerized polyester, a method of dry blending the phosphorus compound with the solid phase polymerized polyester, a polyester master batch chip in which the phosphorus compound is melt kneaded and mixed with the solid phase polymerized polyester chip are mixed. And a method in which a predetermined amount of a phosphorus compound is blended with polyester and melted in an extruder or molding machine to inactivate the catalyst.

  The amount of the phosphorus compound required to completely deactivate the catalyst is at least 5 moles in terms of the residual amount with respect to the catalyst metal content remaining in the polyester.

  Examples of the phosphorus compound used include phosphoric acid, phosphorous acid, phosphonic acid, and derivatives thereof. Specific examples include phosphoric acid, phosphoric acid trimethyl ester, phosphoric acid triethyl ester, phosphoric acid tributyl ester, phosphoric acid triphenyl ester, phosphoric acid monomethyl ester, phosphoric acid dimethyl ester, phosphoric acid monobutyl ester, phosphoric acid dibutyl ester, Phosphoric acid, phosphorous acid trimethyl ester, phosphorous acid triethyl ester, phosphorous acid tributyl ester, methylphosphonic acid, methylphosphonic acid dimethyl ester, ethylphosphonic acid dimethyl ester, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, phenyl -Luphosphonic acid diphenyl ester, etc., and these may be used alone or in combination of two or more.

Moreover, as a method for suppressing the formation of the cyclic trimer in the production process of the polyester film, the polyester is melted and extruded, the melting temperature when producing the sheet is lowered, and the residence time is shortened. Is mentioned as a preferred embodiment. The melting temperature can be adjusted by controlling the temperature of the flow path through which the molten resin passes, and is preferably controlled in the range from the melting point of the polyester to + 30 ° C., and in the range up to + 15 ° C. It is more preferable to control. Further, since the polyester has a slow crystallization rate, it flows without substantially solidifying during the production process in the range up to the melting point of −10 ° C. Therefore, in order to reduce the formation of the cyclic trimer, the resin temperature is set to the above. Controlling to a temperature range is also a preferred embodiment.

  The residence time can be reduced by increasing the flow rate of the resin passing through the volume of the flow path through which the molten resin passes, and the residence time is preferably 60 minutes or less, preferably 30 minutes or less. More preferably.

(Specular reflection film)
The laminated polyester film of the present invention is designed so that the surface layer (A) has a smooth surface. By providing a metal thin film layer on the surface layer (A) surface, light reflectance, particularly regular reflectance, is provided. Therefore, it can be suitably used as a light reflecting member. Therefore, it is a preferred embodiment that the laminated polyester film of the present invention is provided with a metal thin film layer on the surface layer (A) excellent in surface smoothness. That is, by using the laminated polyester film of the present invention as a substrate of a reflective film, forming a metal thin film layer on the surface layer (A) of the laminated polyester film, and forming a specular reflective film having the metal thin film layer as a reflective surface. The effects of the present invention can be exhibited to the maximum. A typical layer structure is shown in FIGS.

  Furthermore, in the laminated polyester film which is a preferred embodiment of the present invention, the surface layer (C) which is the opposite surface of the metal thin film layer is imparted with slipperiness and from the surface layer (C) during film winding. A suitable surface design is made so as to reduce the transfer of dirt and imprints to the surface layer (A). Since these functions are also reflected in a specular reflection film provided with a metal thin film layer, it is suitable as a light reflecting member.

  In the specular reflection film of the present invention, the light reflectance on the surface of the metal thin film layer is preferably 70% or more, and more preferably 75% or more. Moreover, in this invention, in order to evaluate the influence of the reflective characteristic which it has on the layer structure of a laminated polyester film, in each Example (however, except Example 4, Comparative Example 11, Example 7, and Comparative Example 19). A specular reflection film was produced by depositing a metal thin film layer made of aluminum with a thickness of 40 nm on the surface layer (A) of the laminated polyester film. The specular reflection film obtained by forming a metal thin film layer having a thickness of 40 nm on the laminated polyester film of the present invention preferably has a light reflectance of 66% or more on the surface of the metal thin film layer. More preferably, it is 68% or more, and particularly preferably 70% or more. Therefore, by using the specular reflection plate of the present invention as a surface light source reflection plate for LCD, for example, an LCD with high luminance can be obtained.

  The metal which comprises the said metal thin film layer is not limited to the aluminum described above, What is necessary is just a metal with little light absorption, for example, silver, gold | metal | money, platinum, stainless steel, and those alloys can also be tried. By using silver or a silver alloy as the metal, a specular reflection film having a better light reflectivity than when aluminum is used can be obtained. What is necessary is just to select a metal material suitably by market demand. Further, the metal thin film may contain a small amount of a nonmetallic element to the extent that the reflectance is not impaired. The metal thin film may have a single layer configuration or a stacked configuration. The metal thin film layer is generally formed by vacuum vapor deposition, but can also be formed by sputtering or CVD. The thickness of the metal thin film is preferably in the range of 10 to 200 nm.

  Hereinafter, the present invention will be described in detail by way of examples. The film properties obtained in each example were measured and evaluated by the following methods.

(1) Intrinsic viscosity 0.1 g of the chip sample was precisely weighed and dissolved in 25 ml of a mixed solvent of phenol / tetrachloroethane = 6/4 (mass ratio), and measured at 30 ° C. using an Ostwald viscometer. In addition, the measurement was performed 3 times and the average value was calculated | required.

(2) Average particle diameter of particles The particles were observed with a scanning electron microscope (S-510, manufactured by Hitachi, Ltd.), and the magnification was appropriately changed according to the size of the particles. An enlarged copy of the photograph was taken at a magnification of ˜5 mm. Next, the circumference of each particle was traced for at least 200 particles randomly selected. The equivalent circle diameters of the particles were measured from these trace images with an image analyzer, and the average value thereof was taken as the average particle diameter.

(3) Average surface roughness Using a stylus type three-dimensional surface roughness meter (SE-3AK, manufactured by Kosaka Laboratory Ltd.), a needle radius of 2 μm, a load of 30 mg, and a needle speed of 0.1 mm / sec. Under the conditions, the film surface was measured in the longitudinal direction of the film with a cut-off value of 0.25 mm, measured over a measurement length of 1 mm, divided into 500 points at a pitch of 2 μm, and the height of each point was measured with a three-dimensional roughness analyzer ( The product was incorporated into Kosaka Laboratory Ltd., TDA-21). The same operation was performed 150 times continuously at intervals of 2 μm in the width direction of the film, that is, over 0.3 mm in the width direction of the film, and the data was taken into the analyzer. Next, the three-dimensional average surface roughness SRa and the three-dimensional ten-point average roughness SRz were obtained using the analysis device. The unit of SRa and SRz is both μm.
In addition, the measurement was performed 3 times and those average values were employ | adopted.

(4) Number of coarse protrusions of surface layer (A) (4-1) Detection of defects Using the following optical defect detection device, the surface layer (A) surface was observed for 10 pieces of 100 mm × 100 mm laminated polyester film pieces. Then, a defect that was optically recognized as a size of 20 μm or more was detected.
[Optical defect detection method]
A fluorescent lamp of 20 W × 2 lamps is disposed as a projector at 400 mm below the XY table, and a test piece to be measured is disposed on a mask having a slit width of 10 mm provided on the XY table. When light is incident so that the angle formed between the line connecting the projector and the light receiver and the vertical direction of the surface of the test piece is 12 °, if there is a flaw on the test piece at the incident position, that part shines brightly. The amount of light in that portion is converted into an electrical signal by a CCD image sensor camera placed 500 mm above the XY table, the electrical signal is amplified, differentiated, and compared with a threshold (threshold) level and a comparator, resulting in an optical defect. The detection signal is output. Also, using a CCD image sensor camera, an image of coarse projections is input, the video signal of the input image is analyzed by a predetermined procedure, the size of the optical defect is measured, and the defect of 20 μm or larger is measured. Display position. The optical defect is detected on the surface layer (A) of the test piece.
(4-2) Measurement of size and height of coarse protrusion Using the above-described optical defect detection device, an optical defect due to the coarse protrusion of the surface layer (A) was selected from the detected defect portion. Furthermore, it cut out to a suitable magnitude | size and performed Al vapor deposition. Next, the height existing on the surface of the surface layer (A) when observed from the direction perpendicular to the film surface using a non-contact type three-dimensional roughness meter (Micromap 550) is 1 μm or more. The number of coarse protrusions having a maximum diameter of 20 μm or more was measured, and the unit was converted to “pieces / m ² ”.

(5) Film thickness Using a Millitron thickness meter, a total of 15 points were measured, 5 points per sheet, and the average value was determined.

(5) Layer thickness of laminated film The film was cut using a microtome to obtain a cross section perpendicular to the film surface. A sample obtained by coating the cross section with a platinum / palladium alloy by sputtering was used as an observation sample. The cross section of the film was observed using a scanning electron microscope (manufactured by Hitachi, Ltd., model S-510), and a photograph was taken at an appropriate magnification at which the total thickness of the film became one field of view. From this image, the thickness of each layer was measured using a scale. Measurement was performed on three independently prepared cross-sectional samples, and the average value was taken as the layer thickness of the laminated film.

(6) Light transmittance of laminated film According to JIS-B0601-1982, Poic integrating sphere H.264 T. T. Measurement was performed using an R meter (manufactured by Nippon Seimitsu Optics). The smaller this value, the higher the light shielding property.

(7) Apparent density of laminated polyester film Four films were cut into 5.0 cm squares and used as samples. Four samples were stacked, and the total thickness was measured at 10 points using a micrometer with four significant figures, and the total value of the stacked thickness was determined. The average value was divided by 4 and rounded to 3 significant figures to obtain an average thickness per sheet (t: μm). The mass (w: g) of the four samples was measured using an automatic upper pan balance with four significant digits, and the apparent density was determined from the following equation. The apparent density was rounded to 3 significant figures.
Apparent density (g / cm ³ ) = w / (5.0 × 5.0 × t × 10 ⁻⁴ × 4)
= W × 100 / t

(8) Curled value of the laminated polyester film The laminated polyester film was cut into a sheet of 100 mm in the longitudinal direction and 50 mm in the width direction, and after heat treatment at 110 ° C. for 30 minutes under no load, the convex portion of the film was lowered. Measure the vertical distance between the glass plate and the bottom edge of the raised film 4 corners with a ruler in units of 0.5 mm at the minimum scale, and average the measured values at these four locations. Was the curl value. Three samples were prepared and repeatedly measured, and the average value was taken as the curl value.

(9) Scratches on surface layer (A) (i) Scratch detection Sixteen pieces of 250 mm × 250 mm film pieces were evaluated. The evaluation was made for 24 hours after the start of film formation.
A 20 W × 2 fluorescent lamp is arranged as a projector at 400 mm below the XY table, and placed on a mask having a slit width of 10 mm provided on the XY table so that the surface layer (A) of the test piece to be measured is on the upper surface. When light is incident so that the angle formed between the line connecting the projector and the light receiver and the vertical direction of the surface of the test piece is 12 °, if there is a scratch on the test piece at the incident position, that part shines. The amount of light in that portion is converted into an electrical signal by a CCD image sensor camera placed 500 mm above the XY table, the electrical signal is amplified, differentiated, and compared with a threshold (threshold) level and a comparator, resulting in an optical defect. The detection signal is output. In addition, a CCD image sensor camera is used to input an image of a flaw, the video signal of the input image is analyzed according to a predetermined procedure, the size of the optical defect is measured, and the position of the defect of 50 μm or more is displayed. To do. The optical defect is detected on the surface layer (A) of the test piece.

(Ii) Measurement of scratch size From the optical defect portion detected in (i) above, the defect due to the scratch is selected. The test piece was cut into an appropriate size so as to include a portion determined as a scratch by the above method, and a shape observation test piece was collected. Next, the surface layer (A) of the collected test piece is observed from the vertical direction using a three-dimensional shape measuring apparatus TYPE550 manufactured by Micromap, and the size of the scratch is measured. Note that when observed from the direction perpendicular to the surface of the test piece, that is, the film surface, the concavity and convexity of the flaws close to each other within 50 μm are considered as the same flaws, Let the width be the length and width of the wound. Then, the depth (the difference between the height of the highest point and the lowest point) and the length of these scratches are measured. From this result, the number of scratches (pieces / m ² ) having a depth of 1 μm or more and a length of 3 mm or more was determined and judged according to the following criteria.
◎: 30 pieces / m ² or less ○: 31-50 pieces / m ²
Δ: 51 to 100 / m ²
×: 101 pieces / m ² or more

(10) Coefficient of static friction Measured according to JIS K 7125. However, the load cell and the sample were directly connected without using a spring, the mass of the sliding piece was 1.5 kg, and the test speed was 200 mm / min. Each sample was measured three times, and the average value was taken as the coefficient of static friction.

(11) Light reflectivity An integrating sphere is attached to a spectrophotometer (manufactured by Hitachi, Ltd., Spectrophotometer U-3500), and the base of the alumina white plate (manufactured by Hitachi Instrument Service Co., Ltd., 210-0740) is 100%. The line was corrected. The sample was fixed through the mirror surface measuring jig (tilt angle 10 degrees) attached to the apparatus so that the metal thin film surface of the deposited film was on the integrating sphere side. The reflectance was measured in 1 nm increments in the wavelength range of 400 to 700 nm. The measured values of 545 to 555 nm (11 points in total) were averaged to obtain the light reflectance.
In addition, when not providing a metal thin film layer in a lamination | stacking polyester film, a sample is fixed so that the surface of the surface layer (A) of a lamination | stacking polyester film may become an integrating sphere side, According to the said procedure, the said surface layer (A ) Was irradiated with light to determine the light reflectance of the laminated polyester film.

(12) Model evaluation of surface contamination of laminated polyester film in formation process of metal thin film layer (a) Heat treatment A small piece is cut out from any five locations of the film to be measured, and the end is held at 170 ° C. Heated in hot air for 20 minutes. At this time, the film was held so as not to come into contact with other films and instruments, and handled so as not to cause scratches. After heating, it was taken out to room temperature and sufficiently cooled naturally, and then the following observation was performed.

(B) Ratio of Occupied Area of Precipitated Particles on Film Surface First, dust and the like were carefully removed from a film piece to be measured by a static elimination blower. This surface was measured with a non-contact type three-dimensional shape measuring device (manufactured by Micromap; Micromap 557). The optical system used was a mirro-type two-beam interference objective lens (50 ×) and a zoom lens (Body Tube, 0.5 ×), and received light with a 2/3 inch CCD camera using a light source of 5600 Å. The measurement was performed in the WAVE mode, and a field of view of 245 μm square was processed as a digital image of 480 pixels square.

For analysis of the image, surface shape data was obtained by using an analysis software (Micromap 123, version 4.0) and performing detrending in the quartic function mode. Particle analysis was performed from the shape data using analysis software (SX-Viewer, version 3.4.2). After performing planar correction and interpolation using the correction function of the software, protrusions having a longest diameter of 0.01 to 2000 μm and a height of 0.1 μm to 1000 μm were analyzed. As projection analysis parameters, a binarization threshold value 0.01, a rebinarization threshold value 50, and a block size 4 were given, and the projections were binarized and extracted. The area occupied by the protrusions was determined from the obtained analysis results, and the ratio of the area occupied by the protrusions and the area of the visual field (6.0 × 10 ⁴ μm ² ) increased before and after the heat treatment was defined as the occupied area ratio. Note that the measurement was performed at three arbitrary locations on five pieces of film, avoiding clear scratches and foreign matters, and the average value was obtained for a total of 15 fields of view.

(Examples of three-layer or four-layer laminated polyester film)
Example 1
[Production of polyester as raw material for surface layer (A) and polyester layer (A ′)]
The temperature of the esterification reactor was raised, and when it reached 200 ° C., a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was charged. Next, 0.017 parts by mass of antimony trioxide and 0.16 parts by mass of triethylamine were added as a catalyst while stirring the slurry. Further, the temperature was raised by heating, and a pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C.

  Thereafter, the inside of the esterification reaction vessel was returned to normal pressure, and 0.071 part by mass of magnesium acetate tetrahydrate and then 0.014 part by mass of trimethyl phosphate were added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by mass of trimethyl phosphate and then 0.0036 part by mass of sodium acetate were added. The obtained esterification reaction product was transferred to a polycondensation reaction can. Next, the temperature was gradually raised from 260 ° C. to 280 ° C. under reduced pressure, and a polycondensation reaction was performed at 285 ° C. After the polycondensation reaction, filtration was performed with a stainless steel sintered filter having a pore size of 5 μm (initial filtration efficiency: 95%).

  Next, polyethylene terephthalate (PET), which is the polycondensation reaction product, was pelletized in a sealed chamber in which foreign matters having a diameter of 1 μm or more existing in the air were reduced with a hepa filter. Pelletization was performed by a method of extruding molten PET into a cooling water tank from a nozzle of an extruder and cutting the formed strand-like PET resin while flowing cooling water that had been previously filtered (pore size: 1 μm or less). . The obtained PET pellets have an intrinsic viscosity of 0.62 dl / g, an Sb content of 144 ppm, an Mg content of 58 ppm, a P content of 40 ppm, a color L value of 56.2, and a color b value of 1.6. Inert particles and internally precipitated particles were not substantially contained. In Example 1, the same polyester was used for the surface layer (A) and the polyester layer (A ′).

[Preparation of Cavity-Forming Agent-Containing Master Pellet (I)]
As one of the raw materials of the white light-shielding layer (B), a gas phase method polymerization polypropylene (made by Idemitsu Petrochemical Co., Ltd.) having a melt flow rate of 1.5% by weight of polystyrene having a melt flow rate of 1.5 (manufactured by Nippon Polyste, G797N) and a melt flow rate of 3.0. F300SP) 20% by mass, and 60% by mass of polymethylpentene (Mitsui Chemicals Co., Ltd .: TPX DX-820) having a melt flow rate of 180 was mixed with pellets. Next, this pellet mixture was supplied to a twin-screw extruder, sufficiently melted and kneaded, and extruded into a strand shape. The strand was cooled and cut to prepare a cavity forming agent-containing master pellet (I).

[Preparation of titanium oxide-containing master pellets (II)]
As one of the raw materials of the white light-shielding layer (B), 49.5% by mass of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g, anatase type titanium dioxide (manufactured by Fuji Titanium Co., Ltd.) having an average particle size of 0.3 μm (electron microscopy) , TA-300) 50% by mass, and optical brightener (manufactured by Eastman Chemical, OB-1) 0.5% by mass, and the mixture was supplied to a vent type twin screw extruder and pre-kneaded. . Next, the molten polymer was continuously supplied to a vent type single-screw kneader and then sufficiently kneaded to prepare a titanium oxide-containing master pellet (II).

[Preparation of coating solution for forming coating layer (C ′)]
(Preparation of copolymer polyester)
In a stainless steel autoclave equipped with a stirrer, a thermometer, and a partial reflux condenser, 345 parts by weight of dimethyl terephthalate, 211 parts by weight of 1,4-butanediol, 270 parts by weight of ethylene glycol, and tetra-n-butyl titanate 0.5 part by mass was charged, and a transesterification reaction was performed from 160 ° C. to 220 ° C. over 4 hours. Next, 14 parts by mass of fumaric acid and 160 parts by mass of sebacic acid were added, and the temperature was raised from 200 ° C. to 220 ° C. over 1 hour to carry out an esterification reaction. Next, the temperature was raised to 255 ° C., the pressure of the reaction system was gradually reduced, and the mixture was reacted for 1 hour 30 minutes under a reduced pressure of 29.3 Pa to obtain a copolyester. The obtained copolymer polyester was light yellow and transparent, and the weight average molecular weight was 20.000. Moreover, the ratio of the aromatic component by NMR analysis was 70 mol%.

(Preparation of graft modified resin)
A reactor equipped with a stirrer, a thermometer, a reflux device and a quantitative dropping device was charged with 75 parts by mass of copolyester, 56 parts by mass of methyl ethyl ketone and 19 parts by mass of isopropyl alcohol, and heated and stirred at 65 ° C. to dissolve the resin. . After the resin was completely dissolved, 15 parts by weight of maleic anhydride was added to the polyester solution.

  Next, a solution prepared by dissolving 10 parts by mass of styrene and 1.5 parts by mass of azobisdimethylvaleronitrile in 12 parts by mass of methyl ethyl ketone was dropped into the polyester solution at 0.1 ml / min, and stirring was further continued for 2 hours. After sampling for analysis from the reaction solution, 5 parts by mass of methanol was added. Next, 300 parts by mass of water and 15 parts by mass of triethylamine were added to the reaction solution and stirred for 1 hour. Thereafter, the reactor internal temperature was raised to 100 ° C., and methyl ethyl ketone, isopropyl alcohol and excess triethylamine were distilled off to obtain a water-dispersible graft resin. This water-dispersible graft resin) was light yellow and transparent. The acid value of this resin was 1400 eq / t.

(Coating solution adjustment)
40 parts by weight of a 25% by weight aqueous dispersion of the water-dispersible graft resin prepared by the above method, 24 parts by weight of water and 36 parts by weight of isopropyl alcohol are mixed, and a 10% by weight aqueous solution of an anionic surfactant. 20 parts of colloidal silica particles (manufactured by Nissan Chemical Industries Ltd., Snowtex OL, average particle size 40 nm) dispersed in an ion-exchanged water by a homogenizer using 0.6 parts by mass, 1 part by mass of propionic acid, and particles a A dry silica particle (1.8% by weight of an aqueous dispersion, particles b) dispersed in ion-exchanged water by a homogenizer (Nippon Aerosil Co., Ltd., Aerosil OX50, average aggregate particle size 200 nm, average primary particle size 40 nm) 1.1 parts by mass of a 4% by mass aqueous dispersion was added to prepare a coating solution. The mass ratio of the particles a and the particles b is 8, and the content of the particles b is 0.42% by mass with respect to the resin composition of the coating layer.

[Production of laminated polyester film]
A white light-shielding layer (B) comprising a mixture of 7% by mass of the void forming agent-containing master pellet (I), 7% by mass of titanium oxide-containing master pellet (II), and 86% by mass of PET resin having an intrinsic viscosity of 0.62 dl / g As a raw material. Further, the polyester used as the raw material for the surface layer (A) and the polyester layer (A ′) is supplied to two extruders so as to be laminated on both surfaces of the white light-shielding layer (B), and the surface layer (A) It joined with the feed block so that the thickness ratio of / white light-shielding layer (B) / polyester layer (A ′) would be 8/84/8. Subsequently, it was extruded from a three-layer die onto a cooling drum adjusted to 20 ° C. to produce an unstretched film having a layer configuration of two kinds and three layers having a thickness of 1.6 mm.

  The polyester and the mixture of polyester and master pellets were dried in advance in vacuum and then supplied to the extruder. Further, regarding the surface layer (A) and the polyester layer (A ′), a stainless steel sintered filter medium having a filterable particle size of 10 μm (initial filtration efficiency of 95%) is used as a filter material for removing foreign matter of molten PET. Filtration was performed. Further, the opposite surface of the cooling drum was cooled by blowing cold air adjusted to 20 ° C.

  The obtained unstretched film is uniformly heated to 65 ° C. using a heating roll, and 3.4 between two pairs of nip rolls (low speed roll: 1 m / min, high speed roll: 3.4 m / min) having different peripheral speeds. Stretched twice. At this time, as an auxiliary heating device for the film, an infrared heater (rated: 40 W / cm) provided with a gold reflective film in the middle part of the nip roll was placed opposite to both sides of the film (a distance of 1 cm from the film surface). Was heated at 18 W / cm and the opposite surface was heated at 12 W / cm. With respect to all rolls used in the production of the film, the surface roughness of the roll was controlled to be 0.1 μm or less by Ra, and roll cleaners were installed at the preheating inlet and the cooling roll in the longitudinal stretching step. The roll diameter in the longitudinal stretching step was 150 mm, and the film was brought into close contact with the roll using a suction roll, electrostatic contact, and part nip contact apparatus.

The coating liquid for forming the coating layer (C ′) prepared by the above method is microfiltered with a felt type polypropylene filter medium having a filterable particle size of 10 μm (initial filtration efficiency 95%), and the above uniaxial stretching is performed by a reverse roll method. It was applied to one side of the PET film (the surface opposite to the side in contact with the cooling roll) and dried. The coating amount at this time was 0.1 g / m ² . Subsequently, after the coating, the edge of the film was held with a clip, guided to a hot air zone heated to 130 ° C. and dried, and then stretched 4.0 times in the width direction. Next, with the film width fixed, the film was heated by an infrared heater at 250 ° C. for 0.6 seconds to obtain a biaxially oriented laminated polyester film having a thickness of 188 μm and having a coating layer on one side. The characteristic values of the obtained laminated polyester film are shown in Tables 1 and 2. The whiteness of the obtained laminated polyester film was 84.

[Manufacture of specular reflection film]
A mirror reflection film provided with a metal thin film layer (thickness: 40 nm) made of aluminum on the smooth surface layer (A) of the laminated polyester film obtained by the above method was obtained by the following method.

  That is, an aluminum metal piece (10 mg) was fixed to a tungsten filament of a bell jar type vacuum deposition apparatus, and the laminated polyester film was placed 10 cm away from the aluminum piece. After sealing the bell jar, the pressure was reduced to 0.01 Pa using a vacuum pump, and current was applied to the filament to evaporate aluminum. After almost all of the aluminum metal pieces were evaporated by heating for about 15 seconds, the system was cooled down to normal pressure, and the deposited film (specular reflection film) was taken out. Table 2 shows the characteristic values of the obtained specular reflection film.

  Since the laminated polyester film obtained in Example 1 is excellent in the smoothness of the surface layer (A) and the light-shielding property of the white light-shielding layer (B), the obtained specular reflection film is a metal thin film. The light reflectance at the surface of the layer is high. Moreover, since the light which permeate | transmitted the metal thin film layer is shielded by the white light shielding layer (B), even if there is a pinhole in the metal thin film layer, it is not observed. Further, since the coating layer (C ′) is laminated on the polyester layer (A ′), the surface of the coating layer (C ′) which is the outermost layer is appropriately roughened. Therefore, although the surface layer (A) is smooth, it is excellent in slipperiness. Further, since the curling due to heating is suppressed, the handleability of the film is good. Moreover, since the white light-shielding layer (B) contains cavities, the laminated polyester film has a small apparent density and is lightweight.

Comparative Example 1
In Example 1, a laminated polyester film and specular reflection were performed in the same manner as in Example 1 except that the same raw material as that of the white light-shielding layer (B) was used as the raw material of the surface layer (A) and the polyester layer (A ′). A film was obtained. Tables 1 and 2 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Comparative Example 1 is inferior in the smoothness of the surface layer (A) which is the surface on which the metal thin film layer is formed. Therefore, the obtained specular reflection film had a low light reflectivity on the surface of the metal thin film layer, and was low in quality as a light reflecting member.

Comparative Example 2
In Example 1, as a raw material of the layer (B), a laminated polyester film and a specular reflection film were prepared in the same manner as in Example 1 except that the same polyester as the surface layer (A) and the polyester layer (A ′) was used. Obtained. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.

  The laminated polyester film obtained in Comparative Example 2 is excellent in the smoothness of the surface layer (A). However, the laminated polyester film has a high light transmittance because the layer (B) does not have a light shielding property. Therefore, the obtained specular reflection film had a low light reflectance at the surface of the metal thin film layer, and many pinholes were observed in the metal thin film layer. Therefore, it was low quality for the light reflecting member.

  The specular reflection film obtained in this Comparative Example 2 has a surface on the surface of the metal thin film layer as compared with the specular reflection film obtained in Example 1 although the surface layer (A) is excellent in surface smoothness. The light reflectance is inferior. This is presumably because the light transmitted through the metal thin film layer was blocked by the white light-shielding layer (B) and reflected.

Comparative Example 3
In Example 1, as a raw material used for the white light-shielding layer (B), titanium oxide-containing master pellets (II) are not used, and the mixing ratio of the cavity forming agent-containing master pellets (I) is changed to 14% by mass. Obtained a laminated polyester film and a specular reflection film in the same manner as in Example 1. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.

  The laminated polyester film obtained in Comparative Example 3 has a high light transmittance because the light shielding property of the white light shielding layer (B) is low. Therefore, the obtained specular reflection film was not only inferior in light reflectivity on the surface of the metal thin film layer, but also many pinholes were observed in the metal thin film layer. Therefore, the quality of the light reflecting member was low.

Comparative Example 4
In Comparative Example 2, a laminated polyester film and a specular reflection film were obtained in the same manner as in Comparative Example 2 except that the coating layer (C ′) was not formed. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.

  In the laminated polyester film obtained in Comparative Example 4, the polyester layer (A ′) opposite to the surface layer (A) forming the metal thin film layer is smooth as in the surface layer (A). Therefore, in addition to the deterioration in quality described in Comparative Example 2, the slipperiness was remarkably inferior, and the handling properties such as the winding property of the film were also inferior. Therefore, the obtained laminated polyester film had many scratches in the surface layer (A) which is a surface on which the metal thin film layer was formed.

  Further, since the light shielding property of the layer (B) is low, the light transmittance is high. Therefore, the obtained specular reflection film was not only inferior in light reflectivity on the surface of the metal thin film layer, but also many pinholes were observed in the metal thin film layer. Therefore, the quality of the light reflecting member was low.

Comparative Example 5
In Comparative Example 2, when the polyester used for the surface layer (A) and the polyester layer (A ′) is produced, the amount of antimony trioxide added as a polymerization catalyst is doubled, and the polyester used for filtration after completion of the polycondensation reaction is used. A laminated polyester film and a specular reflection film were obtained in the same manner as in Comparative Example 2 except that the pore size of the filter was changed to 20 μm (initial filtration efficiency 95%). The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.
The laminated polyester film obtained in Comparative Example 5 had a large number of coarse protrusions on the surface of the surface layer (A) as well as a decrease in the quality of the film described in Comparative Example 2. Therefore, the quality of the light reflecting member was low.

Example 2
In Example 1, three extruders were used during the production of the laminated polyester film, and instead of the polyester used as the raw material for the polyester layer (A ′), spherical particles having an average particle diameter of 2 μm were used as the raw material for the surface layer (C). A polyethylene terephthalate resin containing 500 ppm of silica particles is used, and the coating layer (C ′) is not formed, and the surface layer A (smooth layer) / white light-shielding layer B / surface layer C (sliding layer) A laminated polyester film and a specular reflection film were obtained in the same manner as in Example 1 except that the layer configuration was changed. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.
The laminated polyester film and the specular reflection film obtained in Example 2 were of high quality similar to those obtained in Example 1, and were highly practical as light reflecting members.

Comparative Example 6
In Example 2, a laminated polyester film composed of two layers and three layers and a specular reflection is the same as in Example 2 except that the same polyester as the surface layer (C) is used as a raw material for the surface layer (A). A film was obtained. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.
The laminated polyester film obtained in Comparative Example 6 was inferior in surface smoothness of the surface layer (A). Therefore, the obtained specular reflection film was inferior in the light reflectivity in the surface of a metal thin film layer. Therefore, the quality of the light reflecting member was low.

Comparative Example 7
In Example 2, a laminated polyester film and a specular reflection film were obtained in the same manner as in Example 2 except that all three layers were changed to use the same polyester as the surface layer (C). The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.

  The laminated polyester film obtained in this Comparative Example 7 had a low light shielding property of the white light shielding layer (B), a high light transmittance, and poor surface smoothness of the surface layer (A). Therefore, the obtained specular reflection film had poor light reflectivity on the surface of the metal thin film layer, and had many pinholes in the metal thin film layer. Therefore, the quality of the light reflecting member was low.

Comparative Example 8
In Comparative Example 6, the layer thickness ratio of the laminated film was adjusted to surface layer (A) / white light-shielding layer (B) / surface layer (C) = 8/90/2, and an unstretched film extruded from a die When cooling with the cooling drum, a laminated polyester film and a specular reflection film were obtained in the same manner as in Comparative Example 6 except that the blowing of cold air adjusted to 20 ° C. was stopped on the opposite surface of the cooling drum. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.

  The laminated polyester film obtained in Comparative Example 8 has a large curl in addition to the deterioration of the quality of the laminated polyester film obtained in Comparative Example 6, and is, for example, under no tension when incorporated into a final product as a light reflector or the like. The handling at the time of work at the site deteriorated. Therefore, the quality of the light reflecting member was low.

Comparative Example 9
In Example 2, the total thickness of the laminated polyester film was changed to 100 μm, and the thickness ratio of each layer was changed to surface layer (A) / white light shielding layer (B) / surface layer (C) = 1/98/1. A laminated polyester film and a specular reflection film were obtained in the same manner as in Example 2 except that. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.
The laminated polyester film obtained in this Comparative Example 9 was inferior in the surface smoothness of the surface layer (A). Therefore, the obtained specular reflection film was inferior in light reflectivity at the surface of the metal thin film layer. Therefore, the quality of the light reflecting member was low.

Comparative Example 10
In Example 1, the coating layer (C ′) is also formed on the surface of the layer (A), and from the side on which the metal thin film layer is formed, coating layer C ′ / layer A / white light-shielding layer B / layer C (layer A). ) / Laminated polyester film and specular reflection film were obtained in the same manner as in Example 1 except that the layers were laminated in this order. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.
The laminated polyester film obtained in Comparative Example 10 was inferior in surface smoothness on the side on which the metal thin film layer was formed. Therefore, the obtained specular reflection film had a light reflectance at the surface of the metal thin film layer. Therefore, the quality of the light reflecting member was low.

Example 3
In Example 1, as a raw material of the white light-shielding layer (B), the cavity forming agent-containing master pellet (I) was not used, and the mixing ratio of the titanium oxide-containing master pellet (II) was changed to 14% by mass. In the same manner as in Example 1, a laminated polyester film and a specular reflection film were obtained. The characteristic values of the obtained laminated polyester film and specular reflection film are shown in Tables 1 and 2.

  The properties related to the light reflection properties of the laminated polyester film and the specular reflection film obtained in Example 3 were high quality as those obtained in Example 1. However, the laminated polyester film obtained in Example 3 had few cavities inside the white light-shielding layer (B). Therefore, the obtained laminated polyester film had a high apparent density and was inferior to the laminated polyester film obtained in Example 1 in terms of weight reduction.

Example 4
When the metal thin film layer made of aluminum was formed on the surface layer (A) by the vacuum deposition method using the laminated polyester film obtained in Example 1, the thickness was changed to 0 nm (no deposition), 41 nm, and 104 nm. The following three types of experiments were conducted. The obtained results are shown in FIG.
(Example 4-1)
Example 4-1 is an experimental example in which the laminated polyester film of Example 1 was used and no metal thin film layer was provided. The light reflectance when the surface layer (A) of the laminated polyester film was irradiated with light was 69%.

(Example 4-2)
Example 4-2 is an experimental example of a specular reflection film in which a metal thin film layer composed of aluminum having a thickness of 41 nm is formed on the surface layer (A) of the laminated polyester film of Example 1 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 72%.
(Example 4-3)
Example 4-3 is an experimental example of a specular reflection film in which a metal thin film layer made of aluminum having a thickness of 104 nm is formed on the surface layer (A) of the laminated polyester film of Example 1 by vacuum deposition. is there. The light reflectivity when the metal thin film layer of the obtained specular reflection film was irradiated with light was 85%.

Comparative Example 11
When the metal thin film layer made of aluminum was formed on the surface layer (A) by the vacuum deposition method using the laminated polyester film obtained in Comparative Example 2, the thickness was 0 nm (no deposition), 29 nm, 70 nm, 98 nm. The following four types of experiments were performed. The obtained results are shown in FIG.

(Comparative Example 11-1)
Comparative Example 11-1 is an experimental example in which the laminated polyester film of Comparative Example 2 was used and no metal thin film layer was provided. The light reflectance when the surface layer (A) of the laminated polyester film was irradiated with light was 8%.
(Comparative Example 11-2)
Comparative Example 11-2 is an example of a specular reflection film in which a metal thin film layer made of aluminum having a thickness of 29 nm was formed on the surface layer (A) of the laminated polyester film of Comparative Example 2 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 37%.

(Comparative Example 11-3)
Comparative Example 11-3 is an experimental example of a specular reflection film in which a metal thin film layer composed of aluminum having a thickness of 70 nm is formed on the surface layer (A) of the laminated polyester film of Comparative Example 2 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 80%.
(Comparative Example 11-4)
Comparative Example 11-4 is an experimental example of a specular reflection film in which a metal thin film layer composed of aluminum having a thickness of 98 nm is formed on the surface layer (A) of the laminated polyester film of Comparative Example 2 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 83%.

  From FIG. 5, the specular reflection film obtained in Example 1 has higher light reflectivity on the surface of the metal thin film layer than the specular reflection film obtained in Comparative Example 2, and the light beam due to the variation in the thickness of the metal thin film layer. The influence of reflectivity is small. This clearly shows that the light leakage through the metal thin film layer is blocked by the white light-shielding layer (B) and reflected.

  The thickness of the metal thin film layer varies depending on the film forming method, but generally has a thickness variation of about 20%. In particular, the thickness of the metal thin film layer tends to be thin at the end portion away from the vapor deposition metal source inside the processing apparatus. However, by providing the white light-shielding layer (B), it is possible to suppress the variation in the light reflectance due to the variation in the thickness of the metal thin film layer. Moreover, the fall of the product yield by the thickness fluctuation | variation of the said metal thin film layer can be suppressed. Furthermore, even if the thickness of the metal thin film layer is reduced, a high light reflectivity can be secured, which is economically superior. Therefore, in the specular reflection film in which the metal thin film layer is provided on the smooth layer (surface layer A) of the laminated polyester film, by providing the white light-shielding layer (B), both the reduction in reflectance variation and the economic efficiency are provided. A remarkable effect is obtained.

(Example of two-layer type laminated polyester film)
Example 5
[Production of polyester for surface layer (A) and white light-shielding layer (B)]
The temperature of the esterification reactor was raised, and when it reached 200 ° C., a slurry consisting of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was charged. Next, 0.017 parts by mass of antimony trioxide and 0.16 parts by mass of triethylamine were added as catalysts while stirring. Further, the temperature was raised by heating, and a pressure esterification reaction was carried out under the conditions of a gauge pressure of 0.34 MPa and 240 ° C.

  Thereafter, the inside of the esterification reaction vessel was returned to normal pressure, and 0.071 part by mass of magnesium acetate tetrahydrate and then 0.014 part by mass of trimethyl phosphate were added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by mass of trimethyl phosphate and then 0.0036 part by mass of sodium acetate were added. The obtained esterification reaction product was transferred to a polycondensation reaction can, gradually heated from 260 ° C. to 280 ° C. under reduced pressure, and subjected to a polycondensation reaction at 285 ° C. After the polycondensation reaction, filtration was performed with a stainless steel sintered filter having a pore size of 5 μm (initial filtration efficiency: 95%).

  Next, polyethylene terephthalate (PET), which is the polycondensation reaction product, was pelletized in a sealed chamber in which foreign matters having a diameter of 1 μm or more existing in the air were reduced with a hepa filter. Pelletization was performed by a method of extruding molten PET into a cooling water tank from a nozzle of an extruder and cutting the formed strand-like PET resin while flowing cooling water that had been previously filtered (pore size: 1 μm or less). . The obtained PET pellets have an intrinsic viscosity of 0.62 dl / g, an Sb content of 144 ppm, an Mg content of 58 ppm, a P content of 40 ppm, a color L value of 56.2, and a color b value of 1.6. Inert particles and internally precipitated particles were not substantially contained.

[Production of low-oligomer-treated polyester]
The polyester obtained by the above method was dried at 160 ° C. under reduced pressure. Next, nitrogen gas containing 400 ppm of ethylene glycol was circulated at 40 liters per hour per 1 kg of the crude polyester. Further, the reaction system was adjusted to a slight pressure of 1.2 kg / cm ² and heat-treated at 215 ° C. for 20 hours to reduce the amount of oligomers. The obtained polyester had an intrinsic viscosity of 0.612 dl / g and a cyclic trimer content of 3400 ppm. In addition, content of the cyclic trimer in polyester before performing the process which reduces an oligomer amount was 9600 ppm.

[Preparation of Cavity-Forming Agent-Containing Master Pellet (I)]
As one of the raw materials for the white light-shielding layer (B), 20 mass% of polystyrene having a melt flow rate of 1.5 (manufactured by Nippon Polyste, G797N) and a vapor phase polymerization polypropylene having a melt flow rate of 3.0 (manufactured by Idemitsu Petrochemical, F300SP) 20% by mass, and 60% by mass of polymethylpentene (manufactured by Mitsui Chemicals, TPX DX-820) having a melt flow rate of 180 were mixed by pellets. Next, this pellet mixture was supplied to a twin-screw extruder, sufficiently melted and kneaded, and extruded into a strand shape. The strand was cooled and cut to prepare a cavity forming agent-containing master pellet (I).

[Preparation of titanium oxide-containing master pellets (II)]
As one of the raw materials for the white light-shielding layer (B), 49.5% by mass of polyethylene terephthalate having an intrinsic viscosity of 0.62 dl / g, an anatase type titanium dioxide having an average particle size of 0.3 μm (electron microscopic method) (manufactured by Fuji Titanium, TA300) 50% by mass and fluorescent whitening agent (manufactured by Eastman Chemical, OB-1) 0.5% by mass were mixed, and the mixture was supplied to a vent type twin screw extruder and pre-kneaded. Next, the molten polymer was continuously supplied to a vent type single-screw kneader and then sufficiently kneaded to prepare a titanium oxide-containing master pellet (II).

[Production of laminated polyester film]
A mixture comprising 7% by mass of the above-mentioned cavity forming agent-containing master pellet (I), 7% by mass of titanium oxide-containing master pellet (II), and 86% by mass of PET resin subjected to oligomer reduction treatment was prepared as a white light-shielding layer (B ). Further, the polyester subjected to the reduction treatment of the oligomer used for the raw material of the surface layer (A) is supplied to two extruders so as to be laminated on the surface of the white light-shielding layer (B), and the surface layer (A) / Joined with a feed block so that the thickness ratio of the white light-shielding layer (B) was 8.7 / 91.3. Subsequently, it was extruded from a two-layer die onto a cooling drum adjusted to 20 ° C. to produce a two-layer unstretched film having a thickness of 1.6 mm.

  The polyester and the mixture of polyester and master pellets were dried in advance in vacuum and then supplied to the extruder. The surface layer (A) was subjected to microfiltration using a stainless steel sintered filter medium having a filterable particle size of 10 μm (initial filtration efficiency of 95%) as a foreign substance removal filter medium for molten PET. Further, the opposite surface of the cooling drum was cooled by blowing cold air adjusted to 20 ° C.

  The obtained unstretched film is uniformly heated to 65 ° C. using a heating roll, and 3.4 between two pairs of nip rolls (low speed roll: 1 m / min, high speed roll: 3.4 m / min) having different peripheral speeds. Stretched twice. At this time, as an auxiliary heating device for the film, an infrared heater (rated: 40 W / cm) provided with a gold reflective film in the middle part of the nip roll was placed opposite to both sides of the film (a distance of 1 cm from the film surface). Was heated at 18 W / cm and the opposite surface was heated at 12 W / cm. With respect to all rolls used in the production of the film, the surface roughness of the roll was controlled to be 0.1 μm or less by Ra, and roll cleaners were installed at the preheating inlet and the cooling roll in the longitudinal stretching step. The roll diameter in the longitudinal stretching step was 150 mm, and the film was brought into close contact with the roll using a suction roll, electrostatic contact, and part nip contact apparatus.

  Next, the film was stretched 4.0 times in the width direction. Subsequently, with the film width fixed, the film was heated by an infrared heater at 250 ° C. for 0.6 seconds to obtain a biaxially oriented laminated polyester film having a thickness of 188 μm. Table 3 shows the characteristic values of the obtained laminated polyester film. The whiteness of the obtained laminated polyester film was 84.

[Manufacture of specular reflection film]
A mirror reflection film provided with a metal thin film layer (thickness: 40 nm) made of aluminum on the smooth surface layer (A) of the laminated polyester film obtained by the above method was obtained by the following method.

  That is, an aluminum metal piece (10 mg) was fixed to a tungsten filament of a bell jar type vacuum deposition apparatus, and the laminated polyester film was placed 10 cm away from the aluminum piece. After sealing the bell jar, the pressure was reduced to 0.01 Pa using a vacuum pump, and current was applied to the filament to evaporate aluminum. After almost all of the aluminum metal pieces were evaporated by heating for about 15 seconds, the system was cooled down to normal pressure, and the deposited film (specular reflection film) was taken out. Table 4 shows the characteristic values of the obtained specular reflection film.

  Since the laminated polyester film obtained in Example 5 is excellent in the smoothness of the surface layer (A) and the light-shielding property of the white light-shielding layer (B), the obtained specular reflection film is a metal thin film. The light reflectance at the surface of the layer is high. Moreover, since the light which permeate | transmitted the metal thin film layer is shielded by the white light shielding layer (B), even if there is a pinhole in the metal thin film layer, it is not observed. Moreover, the surface of the white light-shielding layer (B), which is the opposite surface of the smooth surface layer (A) of the laminated polyester film, is appropriately roughened. Therefore, although the surface layer (A) is smooth, it is excellent in slipperiness. Moreover, since the white light-shielding layer (B) contains cavities, the laminated polyester film has a small apparent density and is lightweight.

  Furthermore, the laminated polyester film obtained in Example 5 is a surface layer (A) in the evaluation of precipitated particles on the surface of the heat-treated laminated polyester film, which is a model evaluation method for surface contamination in the formation process of the metal thin film layer. No precipitation of particles was observed on any of the surfaces of the white light-shielding layer and the surface was high quality.

Comparative Example 12
In Example 5, a laminated polyester film and a specular reflection film were obtained in the same manner as in Example 5 except that the same raw material as the white light-shielding layer (B) was used as the raw material for the surface layer (A). Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Comparative Example 12 is inferior in the smoothness of the surface layer (A) which is the surface on which the metal thin film layer is formed. Therefore, the obtained specular reflection film had a low light reflectivity on the surface of the metal thin film layer, and was low in quality as a light reflecting member.

Comparative Example 13
In Example 5, the same polyester as the surface layer (A) was used as a raw material for the layer (B), and the polyester oligomer was not reduced, and the same as in Example 5, except that the laminated polyester film and mirror surface were used. A reflective film was obtained. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in this Comparative Example 13 was excellent in the smoothness of the surface layer (A). However, since the white light shielding layer (B) has no light shielding property, the light transmittance is high. Therefore, the obtained specular reflection film had low light reflectivity on the surface of the metal thin film layer, and many pinholes were observed in the metal thin film layer. Therefore, it was low quality for the light reflecting member.

  The specular reflection film obtained in this Comparative Example 13 has a surface on the surface of the metal thin film layer as compared with the specular reflection film obtained in Example 5 even though the surface layer (A) is excellent in surface smoothness. The light reflectance is inferior. This is presumably because the light transmitted through the metal thin film layer was blocked by the white light-shielding layer (B) and reflected.

Comparative Example 14
In Example 5, as a raw material of the white light-shielding layer (B), the titanium oxide-containing master pellet (II) is not used, and the mixing ratio of the cavity forming agent-containing master pellet (I) is changed to 14% by mass. In the same manner as in Example 5, a laminated polyester film and a specular reflection film were obtained. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Comparative Example 14 has a high light transmittance because the white light-shielding layer (B) has a low light-shielding property. Therefore, the obtained specular reflection film was not only inferior in light reflectivity on the surface of the metal thin film layer, but also many pinholes were observed in the metal thin film layer. Therefore, the quality of the light reflecting member was low.

Comparative Example 15
In Comparative Example 14, the layer structure of the laminated polyester film was compared except that the coextrusion method was changed so as to have a three-layer structure of surface layer (A) / white light-shielding layer (B) / surface layer (A). In the same manner as in Example 14, a laminated polyester film and a specular reflection film were obtained. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Comparative Example 15 was not only deteriorated in quality in the laminated polyester of Comparative Example 14, but also the opposite surface of the surface layer (A) was smooth as in the surface layer (A). The handling property such as the winding property of the film was inferior. Therefore, there were many scratches in the surface layer (A) which is a surface on which the metal thin film layer is formed. Therefore, the quality of the light reflecting member was low.

Comparative Example 16
In Comparative Example 14, when the polyester used as the raw material for the surface layer (A) was produced, the addition amount of the antimony trioxide as the polymerization catalyst was doubled, and the pore size of the filter for filtering the polyester used after completion of the polycondensation reaction was 20 μm. A laminated polyester film and a specular reflection film were obtained in the same manner as in Comparative Example 14 except that the initial filtration efficiency was changed to 95%. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Comparative Example 16 had a large number of coarse protrusions on the surface of the surface layer (A) as well as a decrease in quality in the laminated polyester of Comparative Example 14. Therefore, the quality of the light reflecting member was low.

Comparative Example 17
In Comparative Example 14, a laminated polyester film and a specular reflection film were obtained in the same manner as in Example 5 except that polyester not subjected to oligomer reduction treatment was used as a raw material for the surface layer (A) and the white light-shielding layer (B). Got. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in this Comparative Example 17 is a heat-treated laminated polyester film that is a model evaluation method for surface contamination in the formation process of the metal thin film layer as well as the quality deterioration in the laminated polyester of Comparative Example 14. In the evaluation of the precipitated particles on the surface, a large number of particles were precipitated on both surfaces of the surface layer (A) and the white light-shielding layer (B), and the quality was low.

Comparative Example 18
In Example 5, the thickness of the laminated polyester film was changed to 100 μm, and the thickness ratio of each layer was changed to Surface layer (A) / White light-shielding layer (B) = 1/99. Similarly, a laminated polyester film and a specular reflection film were obtained. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Comparative Example 18 was inferior in the surface smoothness of the surface layer (A). Therefore, the obtained specular reflection film was inferior in light reflectivity at the surface of the metal thin film layer, and was low quality as a light reflecting member.

Example 6
Intrinsic viscosity containing 20% by mass of anatase-type titanium dioxide (manufactured by Fuji Titanium Industry, TA300) and 0.05% by mass of a fluorescent brightening agent (manufactured by Eastman, OB-1) as a raw material for the white light-shielding layer (B) A laminated polyester film and a specular reflection film were obtained in the same manner as in Example 5 except that 0.62 dl / g of PET was used. Tables 3 and 4 show characteristic values of the obtained laminated polyester film and specular reflection film.
The laminated polyester film obtained in Example 6 was high quality like the laminated polyester film obtained in Example 5. However, since the laminated polyester film obtained in Example 6 does not contain cavities in the white light-shielding layer (B), the apparent density is high, and the laminated polyester film obtained in Example 5 is reduced in weight. It was inferior to the polyester film.

Example 7
When the metal thin film layer made of aluminum was formed on the surface layer (A) by the vacuum vapor deposition method using the laminated polyester film obtained in Example 5, the thickness was 0 nm (no vapor deposition), 38 nm, 55 nm, 94 nm. The following four types of experiments were performed. The obtained result is shown in FIG.

(Example 7-1)
Example 7-1 is an experimental example in which the laminated polyester film of Example 5 was used and no metal thin film layer was provided. The light reflectance when the surface layer (A) of the laminated polyester film was irradiated with light was 69%.

(Example 7-2)
Example 7-2 is an experimental example of a specular reflection film in which a metal thin film layer composed of aluminum having a thickness of 38 nm was formed on the surface layer (A) of the laminated polyester film of Example 5 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 74%.

(Example 7-3)
Example 7-3 is an experimental example of a specular reflection film in which a metal thin film layer made of aluminum having a thickness of 55 nm was formed on the surface layer (A) of the laminated polyester film of Example 5 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 78%.

(Example 7-4)
Example 7-4 is an experimental example of a specular reflection film in which a metal thin film layer composed of aluminum having a thickness of 94 nm was formed on the surface layer (A) of the laminated polyester film of Example 5 by vacuum deposition. is there. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 82%.

Comparative Example 19
When the metal thin film layer made of aluminum was formed on the surface layer (A) by the vacuum deposition method using the laminated polyester film obtained in Comparative Example 13, the thickness was 0 nm (no deposition), 33 nm, 62 nm, 87 nm. The following four types of experiments were performed. The obtained result is shown in FIG.

(Comparative Example 19-1)
Comparative Example 19-1 is an experimental example in which the laminated polyester film of Comparative Example 13 was used and no metal thin film layer was provided. The light reflectance when the surface layer (A) of the laminated polyester film was irradiated with light was 10%.

(Comparative Example 19-2)
Comparative Example 19-2 is a specular reflection film in which a metal thin film layer made of aluminum having a thickness of 33 nm is formed on the surface layer (A) of the laminated polyester film of Comparative Example 13 by vacuum deposition. When the metal thin film layer of the obtained specular reflection film was irradiated with light, the light reflectance was 46%.

(Comparative Example 19-3)
Comparative Example 19-3 is a specular reflection film in which a metal thin film layer made of aluminum having a thickness of 62 nm is formed on the surface layer (A) of the laminated polyester film of Comparative Example 13 by vacuum deposition. The light reflectance when the metal thin film layer of the obtained specular reflection film was irradiated with light was 69%.

(Comparative Example 19-4)
Comparative Example 19-4 is a specular reflective film in which a metal thin film layer made of aluminum having a thickness of 87 nm is formed on the surface layer (A) of the laminated polyester film of Comparative Example 13 by vacuum deposition. When the metal thin film layer of the specular reflection film was irradiated with light, the light reflectance was 80%.

  From FIG. 6, the specular reflection film obtained in Example 5 has a higher light reflectivity on the surface of the metal thin film layer than the specular reflection film obtained in Comparative Example 13, and the light beam due to the variation in the thickness of the metal thin film layer. The influence of reflectivity is small. This clearly shows that the leakage effect of light transmitted through the metal thin film layer is blocked by the white light-shielding layer (B), and the complementary effect of reflection is high.

  The thickness of the metal thin film layer varies depending on the film forming method, but generally has a thickness variation of about 20%. In particular, the thickness of the metal thin film layer tends to be thin at the end portion away from the vapor deposition metal source inside the processing apparatus. However, by providing the white light-shielding layer (B), it is possible to suppress the variation in the light reflectance due to the variation in the thickness of the metal thin film layer. Moreover, the fall of the product yield by the thickness fluctuation | variation of the said metal thin film layer can be suppressed. Furthermore, even if the thickness of the metal thin film layer is reduced, a high light reflectivity can be secured, which is economically superior. Therefore, in the specular reflection film in which the metal thin film layer is provided on the smooth layer (surface layer A) of the laminated polyester film, by providing the white light-shielding layer (B), both the reduction in reflectance variation and the economic efficiency are provided. A remarkable effect is obtained.

  The laminated polyester film of the present invention is formed on the smooth surface (surface layer A) of the laminated film of the present invention with the metal thin film layer serving as a reflective surface as a specular reflective layer, and the metal thin film layer is transmitted through the white light-shielding layer (B). The function to block the reflected light and reflect it is given. As a result, a specular reflection film having a high and uniform light reflectance can be obtained. For this reason, it can be used for specular reflection films with high brightness, particularly for surface light source reflectors for LCDs, and contributes greatly to the industry.

It is explanatory drawing which shows the layer structure of the laminated polyester film which consists of two layers of this invention. It is explanatory drawing which shows the layer structure of the laminated polyester film which consists of three layers of this invention. It is explanatory drawing which shows the layer structure of the laminated polyester film which consists of 4 layers of this invention. It is explanatory drawing which shows the layer structure of the specular reflection film of this invention. In the specular reflection film obtained in Example 4 and Comparative Example 11, it is explanatory drawing which investigated the influence of the thickness of a metal thin film layer with respect to the light reflectivity in the surface of a metal thin film layer. In the specular reflection film obtained in Example 7 and Comparative Example 19, it is explanatory drawing which investigated the influence of the thickness of a metal thin film layer with respect to the light reflectivity in the surface of a metal thin film layer.

Explanation of symbols

1: Laminated polyester film 2: Surface layer (A)
3: White light shielding layer (B)
4: Surface C
5: Surface layer (C)
6: Polyester layer (A ')
7: Coating layer (C ')
8: Metal thin film layer 9: Specular reflection film 10: Irradiation direction 20: Specular reflection film obtained in Example 4 21: Specular reflection film obtained in Comparative Example 11 30: Specular surface obtained in Example 7 Reflective film 31: Specular reflective film obtained in Comparative Example 19

Claims (14)

A polyester composition comprising a layer structure of surface layer (A) / white light-shielding layer (B), wherein the white light-shielding layer (B) contains at least one of a cavity or inorganic particles therein The surface layer (A) is a smooth layer made of polyester whose surface has a three-dimensional ten-point average roughness (SRz) of 0.23 μm or less, and the light transmittance of the laminated polyester film is 20% or less. Ah it is, and the laminated polyester film, at no load condition, laminated polyester film curl value after heat treatment at 110 ° C. 30 minutes and said der Rukoto below 1 mm. A polyester composition comprising a layer structure of surface layer (A) / white light-shielding layer (B), wherein the white light-shielding layer (B) contains at least one of a cavity or inorganic particles therein It includes things, surface layer (a) is a smooth layer the content of either no, or particle-containing particles consisting of polyester is 50ppm or less state, and are light transmittance of 20% or less of the polyester film, and laminated polyester film laminated polyester film of the, in the no load state, the curl value after heat treatment at 110 ° C. 30 minutes and wherein der Rukoto below 1 mm.   The white light-shielding layer (B) contains a cavity formed by stretching polyester and a polyester composition containing a thermoplastic resin incompatible with the polyester in at least one direction. The laminated polyester film according to claim 1 or 2. 3. The laminated polyester film according to claim 1, wherein an apparent density of the laminated polyester film is 0.60 to 1.35 g / cm ³ .   3. The laminated polyester film according to claim 1, wherein a three-dimensional ten-point average roughness (SRz) of the surface of the white light-shielding layer (B) is more than 0.23 μm and 3.0 μm or less.   The total thickness of the said laminated polyester film is 75-300 micrometers, and the thickness of the surface layer (A) is 5-30 micrometers, The laminated polyester film of Claim 1 or 2 characterized by the above-mentioned.   The laminated polyester film has a layer structure of at least three layers of a surface layer (A) / white light-shielding layer (B) / surface layer (C), and the surface layer (C) is a slippery material containing resin and particles. The laminated polyester film according to claim 1 or 2, wherein the SRz of the surface layer (C) is larger than the SRz of the surface layer (A) and is 2.0 µm or less.   The laminated polyester film has a layer structure of surface layer (A) / white light-shielding layer (B) / polyester layer (A ′) / surface layer (C), and the surface layer (C) contains resin and particles. The laminated polyester film according to claim 7, which is a coating layer (C ') comprising the polyester layer (A'), wherein the polyester layer (A ') does not contain particles or is made of polyester having a particle content of 100 ppm or less.   The laminated polyester film according to claim 8, wherein the coating layer (C ') contains particles a having an average particle size of 20 nm or more and less than 150 nm and particles b having an average particle size of 150 nm or more and 600 nm or less.   The total thickness of the laminated polyester film is 100 to 300 μm, the thickness of the surface layer (A) is 5 to 30 μm, the thickness of the surface layer (C), or the polyester layer (A ′) and the coating layer (C ′ ) And the total thickness is 5 to 30 μm. The laminated polyester film according to claim 7 or 8. The laminated polyester film of the when heated at 170 ° C. 20 minutes, the surface layer of the laminated polyester film (A) and the filling ratio of particles deposited on the opposite surface is 0.008μm ^{2 /} μm 2 or less The laminated polyester film according to any one of claims 1, 2, 7, and 8.   Static friction when the surface layer (A) of the laminated polyester film and the white light-shielding layer (B), the surface layer (A) and the surface layer (C), or the surface layer (A) and the coating layer (C ′) are overlaid. The laminated polyester film according to any one of claims 1, 2, 7, and 8, wherein a coefficient is 0.60 or less.   A metal to which light is irradiated using the laminated polyester film according to any one of claims 1, 2, 7, and 8 as a base material of a specular reflection film in which a metal thin film layer is laminated on a surface layer (A) of the film. A laminated polyester film for a specular reflection film, wherein a thin film layer is used as a reflection surface.   It is a specular reflection film which makes the metal thin film layer to which light is irradiated a reflective surface, Comprising: A metal thin film layer is laminated | stacked on the surface layer (A) of the lamination | stacking polyester film in any one of Claim 1, 2, 7, 8 Specular reflection film characterized by being formed.

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